Nutritional and Metabolic Imbalance in Keratoconus

Identification and Verification of Ferroptosis-Related Genes in Keratoconus Using Bioinformatics Analysis

Objective

Keratoconus is a commonly progressive and blinding corneal disorder. Iron metabolism and oxidative stress play crucial roles in both keratoconus and ferroptosis. However, the association between keratoconus and ferroptosis is currently unclear. This study aimed to analyze and verify the role of ferroptosis-related genes (FRGs) in the pathogenesis of keratoconus through bioinformatics.

Methods

We first obtained keratoconus-related datasets and FRGs. Then, the differentially expressed FRGs (DE-FRGs) associated with keratoconus were screened through analysis, followed by analysis of their biological functions. Subsequently, the LASSO and SVM-RFE algorithms were used to screen for diagnostic biomarkers. GSEA was performed to explore the potential functions of the marker genes. Finally, the associations between these biomarkers and immune cells were analyzed. qRT‒PCR was used to detect the expression of these biomarkers in corneal tissues.

Results

A total of 39 DE-FRGs were screened, and functional enrichment analysis revealed that the DE-FRGs were closely related to apoptosis, oxidative stress, and the immune response. Then, using multiple algorithms, 6 diagnostic biomarkers were selected, and the ROC curve was used to verify their risk prediction ability. In addition, based on CIBERSORT analysis, alterations in the immune microenvironment of keratoconus patients might be associated with H19, GCH1, CHAC1, and CDKN1A. Finally, qRT‒PCR confirmed that the expression of H19 and CHAC1 was elevated in the keratoconus group.

Conclusion

This study identified 6 DE-FRGs, 4 of which were associated with immune infiltrating cells, and established a diagnostic model with predictive value for keratoconus.

Keratoconus: exploring fundamentals and future perspectives - a comprehensive systematic review

Background

New developments in artificial intelligence, particularly with promising results in early detection and management of keratoconus, have favorably altered the natural history of the disease over the last few decades. Features of artificial intelligence in different machine such as anterior segment optical coherence tomography, and femtosecond laser technique have improved safety, precision, effectiveness, and predictability of treatment modalities of keratoconus (from contact lenses to keratoplasty techniques). These options ingrained in artificial intelligence are already underway and allow ophthalmologist to approach disease in the most non-invasive way.

Objectives

This study comprehensively describes all of the treatment modalities of keratoconus considering machine learning strategies.

Design

A multidimensional comprehensive systematic narrative review.

Data sources and methods

A comprehensive search was done in the five main electronic databases (PubMed, Scopus, Web of Science, Embase, and Cochrane), without language and time or type of study restrictions. Afterward, eligible articles were selected by screening the titles and abstracts based on main mesh keywords. For potentially eligible articles, the full text was also reviewed.

Results

Artificial intelligence demonstrates promise in keratoconus diagnosis and clinical management, spanning early detection (especially in subclinical cases), preoperative screening, postoperative ectasia prediction after keratorefractive surgery, and guiding surgical decisions. The majority of studies employed a solitary machine learning algorithm, whereas minor studies assessed multiple algorithms that evaluated the association of various keratoconus staging and management strategies. Last but not least, AI has proven effective in guiding the implantation of intracorneal ring segments in keratoconus corneas and predicting surgical outcomes.

Conclusion

The efficient and widespread clinical translation of machine learning models in keratoconus management is a crucial goal of potential future approaches to better visual performance in keratoconus patients.

Trial registration

The article has been registered through PROSPERO, an international database of prospectively registered systematic reviews, with the ID: CRD42022319338.

Screening and identification of genes related to ferroptosis in keratoconus

Corneal keratoconus (KC) is a dilated (ectatic) corneal disease characterized by a central thinning of the cornea, which causes protrusion into a conical shape that seriously affects vision. However, due to the complex etiology of keratoconus, its entire mechanism remains unclear and there is no mechanism-directed treatment method. Ferroptosis is a novel programmed cell death mechanism related to lipid peroxidation, stress, and amino acid metabolism, which plays a crucial role in various diseases. This study aimed to explore the relationship between keratoconus and ferroptosis, to provide new insights into the mechanism of keratoconus development, and potential treatment options based on further elucidation of this mechanism. The corresponding mRNA microarray expression matrix data of KC patients were obtained from GEO database (GSE204791). Weighted co-expression network analysis (WGCNA) and support vector machine recursive feature elimination (SVM-RFE) were selected to screen hub genes, which were overlapped with ferroptosis genes (FRGs) from FerrDb. GO and GSEA were performed to analyze differential pathways, ssGSEA was used to determine immune status, and then, feasible drugs were predicted by gene-drug network. Additionally, we predicted the miRNA and IncRNA of hub genes to identify the underlying mechanism of disease so as to predict treatment for the disease. The epithelial transcriptome from keratoconus tissue mRNA microarray data (GSE204791) was extracted for the main analysis, including eight epithelial cells and eight epithelial control cells. The differential genes that were overlapped by WGCAN, SVM-RFE and FRGs were mainly related to oxidative stress, immune regulation, cellular inflammation, and metal ion transport. Through further analysis, aldo-keto reductase family 1 member C3 (AKR1C3) was selected, and negatively correlated with mature CD56 natural killer (NK) cells and macrophages. Then, gene-drug interaction network analysis and miRNA prediction were performed through the website. It was concluded that four immune-related drugs (INDOMETHACIN, DAUNORUBICIN, DOXORUBICIN, DOCETAXEL) and a miRNA (has-miR-184) were screened to predict potential drugs and targets for disease treatment. To our knowledge, this was the first report of KC being associated with ferroptosis and prompted search for differential genes to predict drug targets of gene immunotherapy. Our findings provided insight and a solid basis for the analysis and treatment of KC.

The impact of UV cross-linking on corneal stromal cell migration, differentiation and patterning

Previous studies have demonstrated that UV cross-linking (CXL) increases stromal stiffness and produces alterations in extracellular matrix (ECM) microstructure. In order to investigate how CXL impacts both keratocyte differentiation and patterning within the stroma, and fibroblast migration and myofibroblast differentiation on top of the stroma, we combined CXL with superficial phototherapeutic keratectomy (PTK) in a rabbit model. Twenty-six rabbits underwent a 6 mm diameter, 70 μm deep phototherapeutic keratectomy (PTK) with an excimer laser to remove the epithelium and anterior basement membrane. In 14 rabbits, standard CXL was performed in the same eye immediately after PTK. Contralateral eyes served as controls. In vivo confocal microscopy through focusing (CMTF) was used to analyze corneal epithelial and stromal thickness, as well as stromal keratocyte activation and corneal haze. CMTF scans were collected pre-operatively, and from 7 to 120 days after the procedure. A subset of rabbits was sacrificed at each time point, and corneas were fixed and labeled in situ for multiphoton fluorescence microscopy and second harmonic generation imaging. In vivo and in situ imaging demonstrated that haze after PTK was primarily derived from a layer of myofibroblasts that formed on top of the native stroma. Over time, this fibrotic layer was remodeled into more transparent stromal lamellae, and quiescent cells replaced myofibroblasts. Migrating cells within the native stroma underneath the photoablated area were elongated, co-aligned with collagen, and lacked stress fibers. In contrast, following PTK + CXL, haze was derived primarily from highly reflective necrotic "ghost cells" in the anterior stroma, and fibrosis on top of the photoablated stroma was not observed at any time point evaluated. Cells formed clusters as they migrated into the cross-linked stromal tissue and expressed stress fibers; some cells at the edge of the CXL area also expressed α-SM actin, suggesting myofibroblast transformation. Stromal thickness increased significantly between 21 and 90 days after PTK + CXL (P < 0.001) and was over 35 μm higher than baseline at Day 90 (P < 0.05). Overall, these data suggest that cross-linking inhibits interlamellar cell movement, and that these changes lead to a disruption of normal keratocyte patterning and increased activation during stromal repopulation. Interestingly, CXL also prevents PTK-induced fibrosis on top of the stroma, and results in long term increases in stromal thickness in the rabbit model.

The mTOR signalling in corneal diseases: A recent update

Corneal diseases affect 4.2 million people worldwide and are a leading cause of vision impairment and blindness. Current treatments for corneal diseases, such as antibiotics, steroids, and surgical interventions, have numerous disadvantages and challenges. Thus, there is an urgent need for more effective therapies. Although the pathogenesis of corneal diseases is not fully understood, it is known that injury caused by various stresses and postinjury healing, such as epithelial renewal, inflammation, stromal fibrosis, and neovascularization, are highly involved. Mammalian target of rapamycin (mTOR) is a key regulator of cell growth, metabolism, and the immune response. Recent studies have revealed that activation of mTOR signalling extensively contributes to the pathogenesis of various corneal diseases, and inhibition of mTOR with rapamycin achieves promising outcomes, supporting the potential of mTOR as a therapeutic target. In this review, we detail the function of mTOR in corneal diseases and how these characteristics contribute to disease treatment using mTOR-targeted drugs.

The Combined Utilization of Epithelial Thickness Mapping and Tomography in Keratorefractive Surgery Screening: One Imaging Modality is Not Sufficient

Increasing popularity and utility of epithelial thickness mapping (ETM) in keratorefractive surgery screening may begin to inappropriately devalue the use of tomography. An increasing body of research suggests that the interpretation of ETM based solely on the corneal resurfacing function may be insufficient to screen and select patients for refractive surgery. ETM and tomography are complementary and, when used together, may provide the safest and most optimal tools for keratorefractive surgery screening.

Analysis of potential impact factors of corneal biomechanics in myopia

PURPOSE

To investigate potential impact factors associated with corneal biomechanical properties in Chinese myopia and further to investigate quantifying corneal biomechanics in clinical work.

METHODS

Three hundred fifty-five eyes from 181 healthy myopic subjects with a mean age of 25.1 ± 9.4 were recruited in this study. Each patient carried out a comprehensive ophthalmic examination, including corneal hysteresis(CH), corneal resistance factor(CRF), central corneal thickness(CCT), axial length(AL), intraocular pressure(IOP), spherical equivalence(SE) and corneal curvature (K). CH and CRF were measured with the ocular response analyzer(ORA). To analyze the corneal biomechanical characteristics of myopia patients and their association with other parameters.

RESULT

The multiple linear regression analysis showed that CH was positively associated with CCT, and corneal curvature (all with P < 0.05) and negatively associated with SE and AL)(all with P < 0.05); CRF was positively correlated with CCT, corneal curvature and IOP(all with P < 0.05), but negatively correlated with SE and AL(all with P < 0.05). The CH and CRF values in children group were both higher than adults group (≥ 18 years old) (P < 0.05), but it attributed to that the CCT of children was thicker than adults. Excluding factor of CCT, there was no significant difference in CH and CRF between children group and adult group. Excluding factor of CCT, there was no significant difference in CH and CRF among different stage of age (age 18-48).

CONCLUSION

The CCT played the most important role of affecting the CH and CRF. The SE, corneal curvature, AL and IOP had a certain influence on corneal biomechanics. Whether the CH and CRF values of individual patient are normal in clinical work, it should refer to the CH and CRF values corresponding CCT sectional range and SE.

Antioxidant and Anti-Inflammatory Effects of Oral Supplementation with a Highly-Concentrated Docosahexaenoic Acid (DHA) Triglyceride in Patients with Keratoconus: A Randomized Controlled Preliminary Study

A prospective, randomized, single-center preliminary study was performed in patients with keratoconus stages I-III (Amsler-Krumeich), who received a high rich docosahexaenoic acid (DHA) (1000 mg/day) supplement for 3 months versus untreated patients. One eye per patient was evaluated. Thirty-four patients were recruited (75% men, mean age 31 years), with 15 randomized to the control group and 19 to the DHA-treated group. Corneal topography variables and plasma biomarkers of oxidative stress and inflammatory status were evaluated. A panel of fatty acids in blood samples was also assessed. There were significant between-group differences in the astigmatism axis, asphericity coefficient, and intraocular pressure in favor of the DHA group. Additionally, between-group significant differences in total antioxidant capacity (TAC), malondialdehyde (MDA), free glutathione (GSH) and GSH/GSSG ratio, as well as reduced values of inflammatory markers, including interleukin (IL)-4, IL-6, and vascular endothelial growth factor (VEGF-A) were found. These preliminary findings support the usefulness of the antioxidant and anti-inflammatory effects of DHA supplementation for targeting underlying pathophysiological mechanisms of keratoconus. Prolonged duration of DHA supplementation may be needed to detect more noticeable clinical changes in corneal topography.

Corneal wound healing and nerve regeneration by novel ophthalmic formulations based on cross-linked sodium hyaluronate, taurine, vitamin B6, and vitamin B12

Introduction: To evaluate the pharmacological profile of ocular formulations based on cross-linked sodium hyaluronate (CL-SH), taurine (Tau), vitamin B6 (Vit B6) and vitamin B12 (Vit B12) using in vitro and in vivo paradigms. Methods: Rabbit corneal epithelial cells were used to assess wound healing and reactive oxygen species (ROS) formation by scratch assay and oxidative stress (0.3 mM H₂O₂; 30 min), respectively with or without ocular formulations exposure. In vivo studies were carried out on albino rabbits to evaluate corneal nerve regeneration and corneal wound healing with or without treatment with six different formulations. Animals were anesthetized, the corneal epithelium was removed, and formulations were topically administered (30 μL/eye; 3 times/day for 6 days). Slit-lamp observation was carried out at different time points. After 6 days the animals were killed, and corneas were collected to evaluate corneal re-innervation by immunohistochemistry of selective neuronal marker β-III tubulin. Results: Formulations containing the concentrations 0.16% or 0.32% of cross-linked sodium hyaluronate, taurine, vitamin B6 and vitamin B12 accelerated corneal wound healing. Cells exposed to H₂O₂ led to significant (p < 0.05) increase of reactive oxygen species concentration that was significantly (p < 0.05) counteract by formulations containing cross-linked sodium hyaluronate (0.32%) and taurine with or without vitamins. The extent of re-innervation, in terms of β-III tubulin staining, was 5-fold greater (p < 0.01) in the eye of rabbits treated with formulation containing 0.32% cross-linked sodium hyaluronate, taurine, vitamins (RenerviX^®) compared with the control group (no treatment). Furthermore, re-innervation elicited by RenerviX^® was significantly greater (p < 0.01) compared with the group treated with the formulation containing 0.32% cross-linked sodium hyaluronate and taurine without vitamins, and with the group treated with the formulation containing 0.5% linear sodium hyaluronate (SH), taurine, and vitamin B12, respectively. Discussion: In conclusion, among the formulations tested, the new ophthalmic gel RenerviX^® was able to contrast oxidative stress, to accelerate corneal re-epithelization and to promote nerve regeneration.

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.

Vitamin D Supplementation Impacts Systemic Biomarkers of Collagen Degradation and Copper Metabolism in Patients With Keratoconus

Purpose

To evaluate the impact of vitamin D (Vit D) supplementation on systemic biomarkers of collagen degradation, inflammation, oxidative stress, and copper metabolism in adolescent patients with keratoconus (KC).

Methods

This was a prospective observational pilot study. Twenty patients (age range, 16-19 years) presenting KC and Vit D insufficiency (<30 ng/mL) were included. Vit D supplementation was prescribed by their general practitioner as per the standard of care. Patients were followed up for 12 months. At each visit, best spectacle-corrected visual acuity (BSCVA), maximal keratometry (Kmax), and thinnest corneal thickness (TCT) were evaluated. The primary outcome of the study was the proportion of patients with Kmax progression of less than 1 D throughout the 12-month follow-up time. Blood samples were collected at different time points to evaluate Vit D levels and systemic markers of collagen degradation, inflammation, oxidative stress, and copper metabolism by ELISA or RT-PCR.

Results

Lower Vit D levels in the plasma were correlated with higher levels of systemic biomarkers of collagen degradation. Vit D supplementation increased the cell availability of copper. Moreover, stabilization of KC progression was found in 60% of patients (72% of eyes) after 12 months with Vit D supplementation. BSCVA, Kmax, and TCT rates remained stable during the observation period.

Conclusions

Our findings support that Vit D administration could affect ocular and systemic biomarkers in KC and illuminate a possible mechanism that can be used to develop new treatment alternatives.

Translational Relevance

Although KC therapy currently relies exclusively on surgical procedures, Vit D supplementation may offer a non-invasive and inexpensive alternative with minimal associated side effects.

[Mineral dysmetabolism in corneal diseases]

Functional status and biological properties of connective tissues significantly depend on the mineral elements involved in their metabolism. Connective tissue portion of the corneal stroma makes up most of its thickness; pathological changes in collagen fibers and the stroma can cause a range of corneal diseases, some of which are specifically associated with disorders of mineral metabolism. The article considers impairments of mineral metabolism as possible pathophysiological mechanisms in certain diseases and disorders of the cornea, and describes in detail the abnormalities associated with mineral dysmetabolism observed in patients with keratoconus.

Distribution of pediatric keratoconus by different age and gender groups

PURPOSE

To evaluate the distribution of pediatric keratoconus patients and the disease severity based on different age and gender groups in China.

MATERIALS AND METHODS

A total of 446 keratoconus eyes in 266 pediatric patients from January 2019 to January 2022 were included in the cross-sectional study. The clinical findings and severity of keratoconus were recorded and Kruskal-Wallis test, chi-squared test, and Cochran-Mantel-Haenszel (CMH) test were used to compare the parameters between different gender and age groups.

RESULTS

The male/female ratio was 353/93 (3.8:1), and the median age was 16 years (range: 6-17 years). Male patients were statistically younger than female patients (P = 0.041). The male/female ratio decreased with age (P for trend = 0.011). The distribution of the topographic keratoconus classification (TKC) stage was significantly different between gender and age groups (all P < 0.05). Male patients had a higher ratio of advanced keratoconus eyes (TKC ≥ 3) than female patients (P < 0.001), and CMH analysis indicated that being a male was a risk factor for advanced keratoconus after controlling for age (odds ratio: 2.581, P < 0.001).

CONCLUSION

Male keratoconus patients were younger, with a higher ratio of advanced keratoconus than female patients in the Chinese pediatric patients evaluated. Multicenter studies with larger sample sizes are necessary in the future.