Higher Expression of Toll-Like Receptors 2 and 4 in Blood Cells of Keratoconus Patiens

Identification of hub genes and molecular pathways in keratoconus by integrating bioinformatics and literature mining at the RNA level

OBJECTIVE

Keratoconus (KC) is a condition characterized by progressive corneal steepening and thinning. However, its pathophysiological mechanism remains vague. We mainly performed literature mining to extract bioinformatic and related data on KC at the RNA level. The objective of this study was to explore the potential pathological mechanisms of KC by identifying hub genes and key molecular pathways at the RNA level.

METHODS

We performed an exhaustive search of the PubMed database and identified studies that pertained to gene transcripts derived from diverse corneal layers in patients with KC. The identified differentially expressed genes were intersected, and overlapping genes were extracted for further analyses. Significantly enriched genes were screened using "Gene Ontology" (GO) and "Kyoto Encyclopedia of Genes and Genomes" (KEGG) analysis with the "Database for Annotation, Visualization, and Integrated Discovery" (DAVID) database. A protein-protein interaction (PPI) network was constructed for the significantly enriched genes using the STRING database. The PPI network was visualized using the Cytoscape software, and hub genes were screened via betweenness centrality values. Pathways that play a critical role in the pathophysiology of KC were discovered using the GO and KEGG analyses of the hub genes.

RESULTS

68 overlapping genes were obtained. Fifty genes were significantly enriched in 67 biological processes, and 16 genes were identified in 7 KEGG pathways. Moreover, 14 nodes and 32 edges were identified via the PPI network constructed using the STRING database. Multiple analyses identified 4 hub genes, 12 enriched biological processes, and 6 KEGG pathways. GO enrichment analysis showed that the hub genes are mainly involved in the positive regulation of apoptotic process, and KEGG analysis showed that the hub genes are primarily associated with the interleukin-17 (IL-17) and tumor necrosis factor (TNF) pathways. Overall, the matrix metalloproteinase 9, IL-6, estrogen receptor 1, and prostaglandin-endoperoxide synthase 2 were the potential important genes associated with KC.

CONCLUSION

Four genes, matrix metalloproteinase 9, IL-6, estrogen receptor 1, and prostaglandin endoperoxide synthase 2, as well as IL-17 and TNF pathways, are critical in the development of KC. Inflammation and apoptosis may contribute to the pathogenesis of KC.

Factors associated with keratoconus in Israel-A cross-sectional population-based study

PURPOSE

To identify potential factors associated with keratoconus.

METHODS

This cross-sectional study included data from Israel's largest healthcare provider for the years 2005-2020. Keratoconus patients and age-matched controls were identified. Demographic factors and comorbid conditions, including smoking, diabetes mellitus, asthma, myalgia, mental retardation, Down syndrome, atopic dermatitis and allergy/allergic rhinitis, were compared between the two cohorts. The independent risk factors associated with keratoconus were determined using a multivariable conditional logistic regression model.

RESULTS

Overall, 145 508 subjects were reviewed of which 13 228 were keratoconus patients. A ten-fold group (n = 132 280) of age-matched control subjects served as controls for comparisons. In multivariable analysis, several factors were found to be significantly associated with keratoconus. Male gender (OR = 1.27, p < 0.001), Arab ethnicity (OR = 1.50, p < 0.001), diabetes (OR = 1.19, p < 0.001), asthma (OR = 1.50, p < 0.001), myalgia (OR = 1.09, p = 0.02), mental retardation (OR = 2.63, p < 0.001), atopic dermatitis (OR = 1.35, p < 0.001) and allergic rhinitis (OR = 1.21, p < 0.001) were significantly associated with keratoconus. Smoking was significantly protective of keratoconus (OR = 0.66, p < 0.001).

CONCLUSIONS

This population-based study reports male gender, Arab ethnicity, diabetes, asthma, myalgia, mental retardation/Down syndrome, atopic dermatitis and allergic rhinitis as factors associated with keratoconus while smoking demonstrates a protective effect. The results of this study could guide enhanced screening strategies and early interventions, particularly for high-risk groups.

The candidate proteins associated with keratoconus: A meta-analysis and bioinformatic analysis

PURPOSE

Keratoconus (KC) is a multifactorial disorder. This study aimed to conduct a systematic meta-analysis to exclusively explore the candidate proteins associated with KC pathogenesis.

METHODS

Relevant literature published in the last ten years in Pubmed, Web of Science, Cochrane, and Embase databases were searched. Protein expression data were presented as the standard mean difference (SMD) and 95% confidence intervals (CI). The meta-analysis is registered on PROSPERO, registration number CRD42022332442 and was conducted in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses statement (PRISMA). GO and KEGG enrichment analysis were performed, as well as the miRNAs and chemicals targeting the candidate proteins were predicted. PPI was analyzed to screen the hub proteins, and their expression was verified by RT-qPCR.

RESULTS

A total of 21 studies were included in the meta-analysis, involving 346 normal eyes and 493 KC eyes. 18 deregulated proteins with significant SMD values were subjected to further analysis. In which, 7 proteins were up-regulated in KC compared with normal controls, including IL6 (SMD 1.54, 95%CI [0.85, 2.24]), IL1B (SMD 2.07, 95%CI [0.98, 3.16]), TNF (SMD 2.1, 95%CI [0.24, 3.96]), and MMP9 (SMD 1.96, 95%CI [0.68, 3.24]). While 11 proteins were down-regulated in KC including LOX (SMD 2.54, 95%CI [-4.51, -0.57]). GO and KEGG analysis showed that the deregulated proteins were involved in inflammation, extracellular matrix (ECM) remodeling, and apoptosis. MMP9, IL6, LOX, TNF, and IL1B were regarded as hub proteins according to the PPI analysis, and their transcription changes in stromal fibroblasts of KC were consistent with the results of the meta-analysis. Moreover, 10 miRNAs and two natural polyphenols interacting with hub proteins were identified.

CONCLUSION

This study obtained 18 candidate proteins and demonstrated altered cytokine profiles, ECM remodeling, and apoptosis in KC patients through meta-analysis and bioinformatic analysis. It will provide biomarkers for further understanding of KC pathogenesis, and potential therapeutic targets for the drug treatment of KC.

Expression of Tissue Inhibitors of Metalloproteinases (TIMP-1, TIMP-2, TIMP-3, TIMP-4) in Blood Serum of Patients with Keratoconus

BACKGROUND

The etiology of keratoconus is unclear. Current evidence suggests that inflammatory and systemic mechanisms might play a role in its pathophysiology. The proper interaction of proteolytic enzymes-matrix metalloproteinases-and their specific tissue inhibitors (TIMPs) within the cornea is essential in maintaining its structure, transparency and healing processes. The aim of the study was to determine the concentration of the TIMPs TIMP-1, TIMP-2, TIMP-3, and TIMP-4 in the blood serum samples of patients with keratoconus compared to the control group.

METHODS

The study encompassed 132 patients, of which 83 people constituted the study group and 49 the control group. The concentration of selected TIMPs was determined using the Human Magnetic Luminex® Performance Assay method.

RESULTS

In the study group, the concentrations of TIMP-1 and TIMP-3 were statistically significantly reduced, and TIMP-2 and TIMP-4 increased compared to the control group. The analysis of individual TIMPs in terms of their usefulness as potential predictors of keratoconus showed high results of diagnostic sensitivity and specificity for all TIMPs, in particular for TIMP-1 and TIMP-2.

CONCLUSION

The above results may indicate systemic disturbances in the TIMPs regulation among keratoconus patients. High diagnostic sensitivity and specificity of all TIMPs, in particular TIMP-1 and TIMP-2, may confirm their participation in the etiopathogenesis of this disease.

Sequence variants contributing to dysregulated inflammatory responses across keratoconic cone surface in adolescent patients with keratoconus

Background

Keratoconus (KTCN) is the most common corneal ectasia resulting in a conical shape of the cornea. Here, genomic variation in the corneal epithelium (CE) across the keratoconic cone surface in patients with KTCN and its relevance in the functioning of the immune system were assessed.

Methods

Samples from four unrelated adolescent patients with KTCN and two control individuals were obtained during the CXL and PRK procedures, respectively. Three topographic regions, central, middle, and peripheral, were separated towards the whole-genome sequencing (WGS) study embracing a total of 18 experimental samples. The coding and non-coding sequence variation, including structural variation, was assessed and then evaluated together with the previously reported transcriptomic outcomes for the same CE samples and full-thickness corneas.

Results

First, pathway enrichment analysis of genes with identified coding variants pointed to "Antigen presentation" and "Interferon alpha/beta signaling" as the most overrepresented pathways, indicating the involvement of inflammatory responses in KTCN. Both coding and non-coding sequence variants were found in genes (or in their close proximity) linked to the previously revealed KTCN-specific cellular components, namely, "Actin cytoskeleton", "Extracellular matrix", "Collagen-containing extracellular matrix", "Focal adhesion", "Hippo signaling pathway", and "Wnt signaling" pathways. No genomic heterogeneity across the corneal surface was found comparing the assessed topographic regions. Thirty-five chromosomal regions enriched in both coding and non-coding KTCN-specific sequence variants were revealed, with a most representative 5q locus previously recognized as involved in KTCN.

Conclusion

The identified genomic features indicate the involvement of innate and adaptive immune system responses in KTCN pathogenesis.

Serum inflammatory biomarkers are associated with increased choroidal thickness in keratoconus

Inflammation may play a significant role in Keratoconus (KC), but the relationship between inflammatory markers and choroidal thickness (CT) is unknown. The purpose of this study was to evaluate serum inflammatory markers and correlate them with the choroidal profile of KC patients and control subjects. Forty patients with KC and 26 age-matched control subjects were enrolled in a cross-sectional case-control study. Choroidal profile was studied with a Spectralis Heidelberg apparatus and venous blood samples were collected. Neutrophil/lymphocyte ratio (NLR), monocyte/HDL ratio (MHR), platelet/lymphocyte ratio (PLR) and systemic immune inflammation index (SII) were calculated. Serum inflammatory biomarkers IL-1, IL-6 and TNF-alfa were also analyzed. KC group presented thicker choroids in each evaluated point when compared to the control group (subfoveal CT 417.38 ± 79.79 vs 299.61 ± 76.13, p < 0.001 for all measured locations). Mean values of NLR, PLR and SII were significantly higher in patients with KC (NLR p = 0.001; PLR p = 0.042; SII p = 0.007). Although KC patients presented higher mean levels of MHR, IL-1, IL-6 and TNF-α than control group, no significant differences were achieved. Positive correlations were found between subfoveal CT and NLR and SII (0.408, p = 0.001 and 0.288, p = 0.019 respectively). The results presented are in favor of a relationship between the increased CT and inflammatory mechanisms in KC patients. The elevated serum inflammatory indices NLR, SII and PLR provide additional evidence of a role for systemic inflammation in the pathophysiology of KC.

The association between keratoconus and allergic eye diseases: A systematic review and meta-analysis

BACKGROUND

To investigate the association between keratoconus (KC) and allergic eye diseases, eye rubbing, and atopy.

METHODS

PubMed, Web of Science, Scopus, and Cochrane databases were searched for studies investigating eye allergy, atopy, and eye rubbing as risk factors for KC up to April 2021. Two authors independently screened all titles and abstracts against the predefined inclusion and exclusion criteria. The study analysed the prevalence of KC and its risk factors, including eye rubbing, family history of KC, atopy, and allergic eye diseases. The National Institutes of Health Study Quality Assessment Tool was used. Pooled data are presented as odds ratios (OR) and 95% confidence intervals (CI). The analysis was conducted using RevMan version 5.4 software.

RESULTS

The initial search yielded 573 articles. After screening, 21 studies were identified for qualitative analysis and 15 for quantitative synthesis. A significant association was found between KC and eye rubbing (OR = 5.22, 95% CI [2.80, 9.75], p < 0.00001), family history of KC (OR = 6.67, 95% CI [4.77, 9.33], p < 0.00001), and allergies (OR = 2.21, 95% CI [1.57, 3.13], p < 0.00001). However, no significant association was found between KC and allergic eye disease (OR = 1.82, 95% CI [0.37, 8.97], p = 0.46), atopy (OR = 1.54, 95% CI [0.58, 4.09], p = 0.39), allergic rhinitis (OR = 0.85, 95% CI [0.54, 1.33], p = 0.47), smoking (OR = 0.96, 95% CI [0.76, 1.21], p = 0.73), and asthma (OR = 1.58, 95% CI [0.99, 2.53], p = 0.05).

CONCLUSION

Significant associations were observed between KC and eye rubbing, family history, and allergy, but not with allergic eye disease, atopy, asthma, and allergic rhinitis.

Biomedical Applications of Lactoferrin on the Ocular Surface

Lactoferrin (LF) is a first-line defense protein with a pleiotropic functional pattern that includes anti-inflammatory, immunomodulatory, antiviral, antibacterial, and antitumoral properties. Remarkably, this iron-binding glycoprotein promotes iron retention, restricting free radical production and avoiding oxidative damage and inflammation. On the ocular surface, LF is released from corneal epithelial cells and lacrimal glands, representing a significant percentage of the total tear fluid proteins. Due to its multifunctionality, the availability of LF may be limited in several ocular disorders. Consequently, to reinforce the action of this highly beneficial glycoprotein on the ocular surface, LF has been proposed for the treatment of different conditions such as dry eye, keratoconus, conjunctivitis, and viral or bacterial ocular infections, among others. In this review, we outline the structure and the biological functions of LF, its relevant role at the ocular surface, its implication in LF-related ocular surface disorders, and its potential for biomedical applications.

Corneal bacterial microbiome in patients with keratoconus using next-generation sequencing-based 16S rRNA gene analysis

PURPOSE

To investigate the corneal bacterial microbiome in patients with keratoconus using next-generation sequencing and develop a new perspective on the pathogenesis of the disease.

METHODS

This prospective observational study included 10 patients with keratoconus who underwent corneal crosslinking procedure and 10 healthy controls who underwent photorefractive keratectomy. Patients included in the study were aged 18 years or older. The demographic and clinical characteristics of participants were recorded. Corneal epithelial samples were collected between March 2021 and June 2021. Isolated bacterial DNA from corneal epithelial samples was analyzed using 16 S ribosomal RNA gene analysis. The relative abundance rates at the phylum and genus levels were calculated. Alpha diversity parameters were assessed.

RESULTS

Eleven phyla and 521 genera of bacteria were identified in all participants. At the phylum level, Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes were most abundant in both groups. There were no statistical differences between the two groups except Bacteriodetes (p < 0.05). At the genus level, the relative abundance rates of twenty bacteria were significantly different between keratoconus and healthy corneas (p < 0.05). Aquabacterium was the most abundant genus in patients with keratoconus, while Shigella was the most abundant genus in healthy controls. Alpha diversity parameters were lower in patients with keratoconus, although the difference did not reach statistical significance (p > 0.05).

CONCLUSIONS

Our preliminary study revealed that there are similarities and differences in the corneal microbiome between keratoconus and healthy individuals. Further research is required on the relationship between the abnormal corneal microbiome composition and the pathogenesis of keratoconus.

Calcitriol modulate post-ischemic TLR signaling pathway in ischemic stroke patients

BACKGROUND

Neuroinflammation is a significant contributor to post-ischemic neuronal death after stroke, and Toll-Like Receptors (TLRs) are one of the essential mediators in many inflammatory pathways. TLRs activate the nuclear factor kappa β (NF-kβ), which promotes the expression of various pro-inflammatory genes such as interleukin (IL-1β) and IL-6. 1,25(OH)2D3, also known as calcitriol, is an active form of vitamin D3 that acts as a neurosteroid compound with anti-inflammatory properties. This study aimed to determine the modulatory effects of calcitriol hormone on post-ischemic immunity response.

METHODS

Neurological tests and conventional blood factors were evaluated in patients with stroke symptoms upon arrival (n = 38) to confirm the stroke. A blood sample was taken from each stroke patient immediately upon admission and again after 24 h. The experimental group was given 10 μg calcitriol orally. The gene expression levels of TLR4, TLR2, NF-kβ, IL-1β, and IL-6 pro-inflammatory factors were measured using real-time PCR. The protein expression of TLR4 and NF-kβ markers was assessed using the flow cytometry technique.

RESULTS

TLR4, NF-kβ, and pro-inflammatory factors IL-1β and IL-6 expression increased significantly after an ischemic stroke, and calcitriol could modulate the TLR4/NF-kβ signaling pathway 24 h after ischemia.

CONCLUSIONS

Calcitriol may be considered a protective reagent after ischemia by reducing the TLR4/NF-kB activation cascade and probably plays a beneficial role in reducing and improving ischemic stroke patients' symptoms.

TRIAL REGISTRATION

Iranian Registry of Clinical Trials identifier: IRCT2017012532174N1.

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.

Immunomodulatory Effect of Human Lactoferrin on Toll-like Receptors 2 Expression as Therapeutic Approach for Keratoconus

Keratoconus (KC) is a corneal disorder whose etiology shares a close relationship with Lactoferrin (LTF) dysregulation and Toll-like Receptors 2 (TLR2) overexpression. This study shows how these two important biomarkers are clinically and molecularly interrelated, increasing knowledge about KC pathophysiology, and opening the door to future therapies. In this prospective clinical study, serum and tear LTF concentrations were quantified in 90 KC patients and 60 controls. A correlation analysis with multiple blood and tear immunoinflammatory mediators, and KC-associated tomographic parameters, was performed. An in vitro study using HEK-BlueTMhTLR2 cell cultures was also conducted to determine the expression and functionality of TLR2 under the influence of LTF treatment. As a result, a LTF decreased was observed in KC patients compared to controls (p < 0.0001), evidencing the strong correlation with TLR2 overexpression at systemic and ocular surface level, with inflammatory mediator upregulation and with KC severity. In stimulated cell cultures, TLR2 expression was decreased using 2 mg/mL of LTF. The levels of secreted embryonic alkaline phosphatase (SEAP) and interleukin-8 (IL-8) were also reduced in supernatants after LTF treatment. As conclusions, the dysregulation of LTF and TLR2 in the ocular surface of KC patients contributes to KC severity by maintaining a detrimental chronic immune−inflammatory state. The immunomodulatory properties of LTF on TLR2 expression suggest its potential as a therapeutic approach for KC.

Identification of Key Genes and Molecular Pathways in Keratoconus: Integrating Text Mining and Bioinformatics Analysis

Purpose. To identify the potential key genes and molecular pathways associated with keratoconus and allergic disease. Methods. The pubmed2ensembl database was used to identify the text mining genes (TMGs) collectively involved in keratoconus and allergic disease. The GeneCodis program was used to perform the Gene Ontology (GO) biological process and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of TMGs. The protein-protein interaction (PPI) network of the TMGs was established by STRING; the significant gene modules and hub genes of PPI were further performed using the Cytoscape software. The DAVID database was used to perform the GO and KEGG analyses of the significant module. Results. In total, 98 TMGs collectively involved in keratoconus and allergic disease were identified. 19 enriched biological processes including 71 genes and 25 enriched KEGG pathways including 59 genes were obtained. A TMG PPI network was constructed, and 51 genes/nodes were identified with 110 edges; 3 most significant modules and 12 hub genes were chosen from the PPIs. GO enrichment analysis showed that the TMGs were primarily associated with collagen catabolic process, extracellular matrix organization and disassembly, cell adhesion and migration, collagen-containing extracellular matrix, extracellular matrix, and structure organization. KEGG pathway analysis showed that these DEGs were mainly involved in the IL-17 signaling pathway, inflammatory bowel disease, rheumatoid arthritis, allograft rejection, T cell receptor signaling pathway, cytokine-cytokine receptor interaction, and TNF signaling pathway. Conclusions. The results revealed that IL10, IL6, MMP9, MMP1, HGF, VEGFA, MMP3, MMP2, TGFB1, IL4, IL2, and IFNG were potential key genes involved in keratoconus. IL-17 signaling pathway was the potential pathways accounting for pathogenesis and development of keratoconus.

Lactoferrin and its nano-formulations in rare eye diseases

Lactoferrin (LF) is an iron-binding glycoprotein released from mucous secreting cells and neutrophils. LF can be used in a broad range of eye diseases related to the retina, cornea, and optic nerve. The retina is particularly affected by oxidative stress inside the photoreceptor being constantly exposed to light which induces accumulation of reactive oxygen species (ROS) in the retinal pigmented epithelium (RPE) causing damage to photoreceptor recycling. Retinitis pigmentosa (RP) and macular degeneration are inherited retinopathies that consist of different disease-causing genes, that cause mutations with highly varied clinical consequences. Age-related macular degeneration is a chronic disease of the retina and one of the major causes of sight loss. This review provides an application of lactoferrin and LF-based nano-formulations or nanoparticles in the field of retinal diseases or corneal diseases such as retinitis pigmentosa, retinoblastoma, age-related macular degeneration (AMD), keratoconus and uveitis. Several studies have found that lactoferrin's antibacterial activity is not limited to its iron sequestration, but also its ability as a nanoparticle that acts as a carrier to deliver drugs by crossing the blood-retina barrier (BRB) and its involvement in cell cycle control, which is not possible by many transferrin proteins.

Shotgun Proteomics for the Identification and Profiling of the Tear Proteome of Keratoconus Patients

Purpose

The qualitative approach followed in this study aims to obtain an extensive view of the keratoconus (KC) tear proteome, which could highlight proteins previously undetected and enlarge our knowledge of the disease's pathophysiology.

Methods

Twenty-five patients diagnosed with KC and 25 control subjects were studied in a prospective, cross-sectional study. KC screening examinations, including clinical and tomographic examinations, were performed on all participants. Tear samples were collected using Schirmer strips and analyzed by liquid chromatography-tandem mass spectrometry in a data-dependent workflow. A spectral count was used as a semiquantification tool. The tear proteomes of both groups were identified and profiled, and the functional interactions and biological characterization of differential proteins were analyzed using in silico tools.

Results

We identified a total of 232 proteins, of whom 133 were expressed in both groups’ samples; 41 were observed only in control samples and 58 were identified just in tears of patients with KC. A semiquantitative analysis showed the dysregulation of 17 proteins in the KC samples. An in silico analysis linked proteins only expressed in KC samples to oxidative stress, skin development, and apoptosis. The dysregulation of proteins involved in iron transport, inflammation, oxidative stress, and protease inhibition was observed in the semiquantitative results.

Conclusions

A shotgun analysis showed that the tear proteome of patients with KC differed from controls by more than one-third of the total proteins identified, highlighting the relationship of the proteins only expressed in KC tears with processes of cell death, oxidative damage, and inflammation. The underexpression of proteins involved in iron pathways might support the iron imbalance as a contributing factor to cellular damage and death in KC disease.

Biochemical and molecular alterations and potential clinical applications of biomarkers in keratoconus

Keratoconus (KC) is a complex multifactorial corneal ectatic disorder, with disease onset commonly in the second-third decades significantly affecting quantity, quality of vision, and quality of life. Several pathways and factors such as eye rubbing, inflammatory, oxidative, metabolic, genetic, and hormonal among others have been studied in the last two decades. However, the management of KC is still based on a few "one-size fits all" approaches and is predominantly guided by topo/tomographic parameters. Consideration of the several novel factors which have the potential to be biomarkers in addressing several unanswered questions in the disease process could help in the better predictive ability of progression or vision loss and customization of treatment options. This article delves into the understanding of these novel factors or biomarkers based on the pathogenesis of KC and features a special focus on their potential clinical applications and their future role in personalized medicine.

The association between keratoconus and allergic eye diseases: A systematic review and meta-analysis

BACKGROUND

To investigate association between keratoconus and allergic eye diseases, eye rubbing, and atopy.

METHODS

PubMed, Web of Science, Scopus, and Cochrane were searched for relevant published studies from inception to April 2021 without restrictions or filters. We included case-control, cohort, and cross-sectional studies that investigated eye allergy, atopy, or eye rubbing as possible risk factors for KC. Two authors independently screened all titles and abstracts against predefined inclusion and exclusion criteria. This study analysed keratoconus prevalence and risk factors including eye rubbing, family history of keratoconus, atopy, and allergic eye diseases. The National Institute of Health Study Quality Assessment tool was utilised. Pooled data were presented as odds ratio (OR) and 95% confidence intervals (CI). Analysis was conducted using RevMan version 5.3 software.

RESULTS

Out of 573 articles, we excluded 161 duplicates than 361 articles by title and abstract screening. The remaining 51 articles underwent full-text screening, and 29 articles were excluded. Twenty-one studies were included in the qualitative synthesis and fifteen for quantitative synthesis. There was no significant association found between KC and allergic eye diseases (OR = 1.03, 95% CI [0.96, 1.11], p = 0.45), eye rubbing (OR = 1.59, 95% CI [0.70, 3.63], p = 0.27), or atopy (OR = 1.08, 95% CI [0.80, 1.44], p = 0.62).

CONCLUSION

No significant association was observed between KC and allergic eye disease, eye rubbing, or atopy. Further prospective studies are needed to clarify and validate these findings.

Comprehensive Transcriptome Analysis of Patients With Keratoconus Highlights the Regulation of Immune Responses and Inflammatory Processes

Keratoconus (KTCN), characterized by the steeper curvature of the cornea and the thinner central corneal thickness, was a degenerative corneal ectasia with ambiguous etiology and mechanism. We aim to reveal underlying pathological mechanisms of KTCN by multi-level transcriptomic, integrative omics analyses. We performed RNA-sequencing on corneal epithelial samples from seven patients and seven control donors, as well as peripheral matched blood samples from three of the patients and three control donors. After RNA extraction, library construction, and sequencing, differentially expressed genes and splicing events were identified, followed by over-representation analysis. In total, 547 differential expressed genes were identified in KTCN corneal epithelial samples, which were mainly enriched in immune responses and inflammatory processes. WGCNA module analysis, the transcriptomic analysis of peripheral blood samples, multiple omics data, and the meta-analysis of GEO samples confirmed the involvement of immune and inflammatory factors. Besides, 190 and 1,163 aberrant splicing events were identified by rMATS combined with CASH methods in corneal epithelial and blood samples with KCTN. In conclusion, this comprehensive transcriptome analysis of KTCN patients based on patients’ tissue and blood samples uncovered a significant association between immune-inflammatory genes and pathways with KCTN, highlighting the contribution of the perturbed immune signaling to the pathogenesis of KCTN. Our study suggested the importance of measures to control inflammation in the treatment of KCTN.

Potential underlying genetic associations between keratoconus and diabetes mellitus

Background Keratoconus (KC) is the most common ectatic corneal disease, characterized by significantly localized thinning of the corneal stroma. Genetic, environmental, hormonal, and metabolic factors contribute to the pathogenesis of KC. Additionally, multiple comorbidities, such as diabetes mellitus, may affect the risk of KC. Main Body Patients with diabetes mellitus (DM) have been reported to have lower risk of developing KC by way of increased endogenous collagen crosslinking in response to chronic hyperglycemia. However, this remains a debated topic as other studies have suggested either a positive association or no association between DM and KC. To gain further insight into the underlying genetic components of these two diseases, we reviewed candidate genes associated with KC and central corneal thickness in the literature. We then explored how these genes may be regulated similarly or differentially under hyperglycemic conditions and the role they play in the systemic complications associated with DM. Conclusion Our comprehensive review of potential genetic factors underlying KC and DM provides a direction for future studies to further determine the genetic etiology of KC and how it is influenced by systemic diseases such as diabetes.

Ocular Complications of Obstructive Sleep Apnea

Obstructive sleep apnea (OSA), the most common form of sleep-disordered breathing, is characterized by repetitive episodes of paused breathing during sleep, which in turn induces transient nocturnal hypoxia and hypercapnia. The high prevalence of OSA and its associated health consequences place a heavy burden on the healthcare system. In particular, the consequent episodic oxygenic desaturation/reoxygenation series and arousals from sleep in patients with OSA have the potential to trigger oxidative stress, elevated systemic inflammatory responses, and autonomic dysfunction with sympathetic activation. Given these adverse side-effects, OSA is highly correlated to many eye diseases that are common in everyday ophthalmic practices. Some of these ocular consequences are reversible, but they may permanently threaten a patient’s vision if not treated appropriately. Here, this article seeks to review the ocular consequences and potential pathophysiologic associations in patients with OSA. Understanding these OSA-related eye diseases may help clinicians provide comprehensive care to their patients.

Case Report: Double Intrastromal Corneal Ring Segment and Posterior Chamber Phakic Intraocular Lens Implantation

SIGNIFICANCE

Keratoconus can manifest asymmetrically, affecting binocularity and becoming a refractive problem that is sometimes complex to solve. We propose a therapeutic approach for correction of keratoconus based on parallel implantation of a second intrastromal corneal ring segment (ICRS).

PURPOSE

This study aimed to improve the refractive status of a patient affected with advanced bilateral keratoconus using implantation of a second ICRS and a phakic intraocular lens.

CASE REPORT

A 44-year-old man came to our clinic requesting a refractive solution for his visual impairment. He had been diagnosed with bilateral severe keratoconus categorized by the Amsler-Krumeich classification scale as grade III (right eye) and grade II (left eye). He had previously undergone corneal cross-linking and implantation of ICRS (Intacs) in both eyes. Significant anisometropia was present between the eyes, and the patient also complained of poor quality of vision. We decided to implant a posterior chamber phakic collamer lens in his right eye and to insert a new ICRS (Keraring) deep and parallel to the previous one in his left eye. We aimed to prevent anisometropia in his right eye and to further regularize the affected cornea in his left eye. Refractive symmetry was achieved, and vision was optimized after surgery.

CONCLUSIONS

In a patient with keratoconus, refractive surgery should be performed from a bilateral perspective. Specific cases of keratoconus can be managed by parallel implantation of a second ICRS.

Implication of Toll/IL-1 receptor domain containing adapters in Porphyromonas gingivalis-induced inflammation

Periodontitis is induced by periodontal dysbiosis characterized by the predominance of anaerobic species. TLRs constitute the classical pathway for cell activation by infection. Interestingly, the Toll/IL-1 receptor homology domain adapters initiate signaling events, leading to the activation of the expression of the genes involved in the host immune response. The aim of this study was to evaluate the effects of Porphyromonas gingivalis on the expression and protein-protein interactions among five TIR adapters (MAL, MyD88, TRIF, TRAM and SARM) in gingival epithelial cells and endothelial cells. It was observed that P. gingivalis is able to modulate the signaling cascades activated through its recognition by TLR4/2 in gingival epithelial cells and endothelial cells. Indeed, MAL-MyD88 protein-protein interactions associated with TLR4 was the main pathway activated by P. gingivalis infection. When transient siRNA inhibition was performed, cell viability, inflammation, and cell death induced by infection decreased and such deleterious effects were almost absent when MAL or TRAM were targeted. This study emphasizes the role of such TIR adapter proteins in P. gingivalis elicited inflammation and the precise evaluation of TIR adapter protein interactions may pave the way for future therapeutics in both periodontitis and systemic disease with a P. gingivalis involvement, such as atherothrombosis.

The Role of Atopy in the Choroidal Profile of Keratoconus Patients

Purpose

Although classically classified as a non-inflammatory condition, an inflammatory basis for keratoconus (KC) appears to be a growing evidence. Recently, it has been shown that KC patients have an increased choroidal thickness (CT). Among inflammatory disorders, atopy has been associated with KC development; therefore, the aim of this study was to evaluate if the increased CT in patients with KC is related to atopy.

Methods

This is an analytical cross-sectional study of patients with KC. Patients were classified as atopic and non-atopic according to their atopy history (allergic rhinoconjunctivitis (AR), asthma (AA) and/or atopic dermatitis (AD)) and were also classified based on their eye rubbing habits. Choroidal profile of all subjects was evaluated using a Spectralis optical coherence tomography (OCT) device with enhanced depth imaging (EDI) mode. CT was measured and compared between groups at the center of the fovea and at 500 µm intervals along a horizontal section. A multivariable analysis, adjusted for sex, age, spherical equivalent, history of medication and atopy, was performed to assess the influence of atopy in CT.

Results

Of the 80 patients included, 51 were atopic and 29 non-atopic. Atopic patients showed a thicker choroid in every measured location than the non-atopic patients (mean subfoveal CT 391.53 µm vs 351.17 µm, respectively), although the differences were not statistically different. The multivariable analysis revealed that being atopic makes the choroid statistically thicker, on average, 55.14 µm, when compared to non-atopic patients (p=0.043). Furthermore, patients who are frequent eye rubbers have significantly thicker choroids than non-rubbers (p=0.004).

Conclusion

Although some results do not reach statistical significance, atopic KC patients seem to have thicker choroids compared with non-atopic KC patients, suggesting a possible role for atopy in the choroidal profile of KC. This constitutes a completely new sight in this field of research that needs further investigation.

Corneal and conjunctival alteration of innate immune expression in first-degree relatives of keratoconus patients

PURPOSE

The innate immune toll-like receptors 2 (TLR2) and 4 (TLR4) may play a key role in the physiopathology of keratoconus (KC). Therefore, the aim of this study was to compare TLR2/TLR4 expression in corneal and conjunctival epithelial cells between healthy first-degree relatives of patients with KC and healthy controls as well as KC patients.

METHODS

Case-control study in 72 healthy eyes of 36 control subjects, 53 eyes of 27 first-degree relatives, and 109 eyes with KC (60 patients). All participants were subjected to a clinical, topographic, aberrometric, and tomographic examination with extraction of corneal and conjunctival epithelial cells through scraping. TLR2/TLR4 expression was measured by flow cytometry, and was compared among controls, first-degree relatives, and KC patients. The relationship between TLR expression and epidemiological-clinical variables or topographic-aberrometric-tomographic parameters was also analyzed.

RESULTS

Mean TLR2/TLR4 expression showed a significant gradual increase among groups: controls < first-degree relatives < KC patients. Mean expression of TLR2 in corneal epithelial cells and both TLR2/TLR4 in conjunctival epithelial cells were significantly higher in relatives than in controls (p = 0.026, p < 0.001, and p = 0.031, respectively). Sex, age, allergic disease, eye itching, rubbing, and topographic-aberrometric-tomographic parameters were not associated to TLR2/TLR4 expression in relatives. TLR2 conjunctival expression was independently associated to relatives (OR 1.001; CI 95% 1.000-1.002, p = 0.043) after adjustment by sex, age, and rubbing.

CONCLUSION

TLR2 and TLR4 are overexpressed in corneal and conjunctival epithelial cells of KC relatives compared with controls. Both biomarkers may monitor early ocular changes in first-degree relatives who not show any abnormal clinical-topographic-aberrometric-tomographic parameters.

Association between atopic keratoconjunctivitis and the risk of keratoconus

PURPOSE

To investigate the risk of keratoconus (KCN) in patients with atopic keratoconjunctivitis (AKC).

METHODS

This nationwide, retrospective, matched cohort study included 186 202 newly diagnosed AKC patients who were identified by the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM), code 372.05, and selected from the Taiwan National Health Insurance Research Database. The age- and sex-matched control group included 186 202 non-AKC patients selected from the Taiwan Longitudinal Health Insurance Database 2000. Patient information was collected between 1 January 2004 and 31 December 2011, and both groups of patients were tracked from the index date until December 2013. The incidence and risk of KCN (ICD-9-CM, code 371.6) were compared between the groups. A Cox proportional hazard regression analysis was performed to obtain the adjusted hazard ratio (HR) for KCN. The cumulative KCN incidence rate was calculated with the Kaplan-Meier analysis.

RESULTS

In total, 62 AKC patients and 26 controls developed KCN during the follow-up period. The incidence rate of KCN was 2.49 times (95% confidence interval [CI] = 1.57-3.93; p < 0.0001) higher in AKC patients than in controls. After adjusting for potential confounders, AKC patients were 2.25 times more likely to develop KCN than controls (adjusted HR, 2.25; 95% CI = 1.41-3.58; p < 0.05).

CONCLUSION

Atopic keratoconjunctivitis (AKC) patients had an increased risk of developing KCN. Therefore, AKC patients should be advised of this risk.

Design, Optimization, and Characterization of Lactoferrin-Loaded Chitosan/TPP and Chitosan/Sulfobutylether-β-cyclodextrin Nanoparticles as a Pharmacological Alternative for Keratoconus Treatment

This research study describes the design, optimization, and characterization of two different types of chitosan-based nanoparticles as novel drug delivery systems of a protein drug, lactoferrin. A preclinical consistent base was obtained for both nanosystems, being considered as the first pharmacological treatment for keratoconus as an alternative to current invasive clinical methods. Both types of nanoparticles were obtained via the ionotropic gelation technique. The size and morphology of the nanoparticles were studied as a function of the preparation conditions. A mean size of 180.73 ± 40.67 nm, a size distribution [polydispersity index (PDI)] of 0.170 ± 0.067, and positive ζ-potential values, ranging from 17.13 to 19.89 mV, were achieved. Lactoferrin was successfully incorporated into both types of nanocarriers. In vitro release profiles showed a lactoferrin enhanced, prolonged, and controlled delivery from the polymeric matrix. These formulations also demonstrated no stability or cytotoxicity problems, as well as appropriate mucoadhesive properties, with a high permanence time in the ocular surface. Thus, both types of nanoparticles may be considered as nanocarriers for the controlled release of lactoferrin as novel topical ophthalmic drug delivery systems.

Biochemical Markers and Alterations in Keratoconus

Keratoconus (KC) is a corneal ectatic condition characterized by focal structural changes, resulting in progressive thinning, biomechanical weakening, and steeping of the cornea that can lead to worsening visual acuity due to irregular astigmatism and corneal scarring in more advanced cases. It is a relatively common ectatic disease of the cornea predominantly affecting the younger population. Despite its worldwide prevalence, its incidence is rather varied with a higher incidence among the Middle Eastern and South Asian population. Dysregulated corneal extracellular matrix remodeling underlies KC pathogenesis. However, a lack of absolute clarity regarding the factors that initiate and drive progression poses a significant challenge in its prevention and management. KC is a complex multifactorial disease as it is associated with a wide variety of etiological factors such as environmental stimuli/insults, oxidative stress, genetic predisposition, comorbidities, and eye rubbing. A series of studies using corneal tissues (epithelium, stroma), cultured corneal fibroblasts/keratocytes, tear fluid, aqueous humor, and blood from KC subjects has reported significant alterations in various biochemical factors such as extracellular matrix components, cellular homeostasis regulators, inflammatory factors, hormones, metabolic products, and chemical elements. It has become apparent that alterations in the biochemical mediators (related to various etiologies) could contribute to KC pathogenesis by altering the dynamics of extracellular matrix remodeling events such as collagen deposition, degradation, and cross-linking in the cornea. Determining key disease contributing biochemical mediators would aid in disease monitoring, prediction or abatement of disease progression, and development of targeted therapeutics to improve disease prognosis.

Increased choroidal thickness is not a disease progression marker in keratoconus

The recent findings of increased Choroidal Thickness (CT) in Keratoconus (KC) patients raised the question of whether CT could be an indicator of progressive KC. To test this hypothesis, we evaluated and compared the choroidal profile in progressive and non-progressive KC. We ran a cross-sectional observational study in 76 patients diagnosed with KC, age 14–30, to assess KC progression. Progression was defined as when at least two of the studied variables confirmed progression (Kmax, Km, PachyMin, D-Index, Astig, K2, 3 mm PCR). Included patients performed a Spectralis Optical Coherence Tomography (OCT) with enhanced depth image (EDI) technology to evaluate choroidal profile. Choroidal measurements were taken subfoveally and at 500 µm intervals from the fovea, in 7 different locations, and compared between groups. Multivariate linear regression analyses were also performed to assess the influence of CT in KC progression. Thirty-six eyes (47.4%) were classified as KC progressors. The mean subfoveal CT observed in the total sample was 382.0 (± 97.0) μm. The comparison between groups (progressive and non-progressive KC) showed no differences in the locations evaluated (mean subfoveal CT difference between groups was 2.4 μm, p = 0.915). In the multivariate analysis CT seems not be influenced by KC progression (B = 6.72 μm, 95% CI − 40.09 to 53.53, p = 0.775). Assessment of choroidal profile does not appear to be a useful tool to differentiate progressive and non-progressive KC. Further research is needed in order to better understand the role of choroid in KC.

Toll-like receptors as diagnostic targets in pellucid marginal degeneration

The main purpose of this study is to evaluate the diagnostic role of Toll-like receptors 2 (TLR2) and 4 (TLR4) expression in corneal and conjunctival epithelial cells of eyes with pellucid marginal degeneration (PMD) compared to keratoconus patients (KC) and control subjects. A prospective case-control study in 29 PMD eyes, 109 KC eyes and 72 healthy eyes was done. All participants were subjected to a clinical, topographic, aberrometric and tomographic exam with extraction of corneal and conjunctival epithelial cells through scraping. The TLR2 and TLR4 expression was measured with flow cytometry. Receiver operating characteristic (ROC) curve analysis was used to determine the most appropriate cutoff point for predicting the risk of PMD and KC. Correlations between TLR2/TLR4 expression and the severity of PMD/KC were evaluated. A TLRs follow-up review was made 19 ± 4 months after to the first review. As result, mean expression of TLR2 and TLR4 in both corneal and conjunctival epithelial cells was significantly higher in eyes with corneal ectasia (PMD and KC) than in control eyes (all p < 0.05). Conjunctival TLR4 expression showed the highest capacity to diagnose the existence of PMD (odd ratio 42.84; 95% confidence interval:6.20-296.20; p < 0.0001) after adjusting by eye rubbing and steeper corneal meridian. Moreover, we found an association between the TLR2/TLR4 overexpression with the severity of the PMD and KC measured by corneal topographic, aberrometric and tomographic quantitative parameters (all p < 0.05). Differences on TLR2/TLR4 expression between study groups were maintained during the follow-up period. In conclusion, the TLR2/TLR4 overexpression in corneal and conjunctival epithelial cells of PMD and KC patients compared to healthy control subjects have demonstrated their role as diagnostic target in both corneal ectatic disorders.

Analysis of Choroidal Vascularity Index in Keratoconus Patients Using Swept-Source Optical Coherence Tomography-Based Binarization Techniques

PURPOSE

To analyse the vascular density of the choroid in a keratoconus (KC) population using swept-source optical coherence tomography (SS-OCT).

METHODS

Prospective, noninterventional study that analysed 97 eyes from 52 KC patients and 145 eyes from 89 healthy controls. The sample was divided in four different age groups. Inclusion criteria were topographic diagnosis of KC using Pentacam, axial length shorter than 26 mm, good quality of the images, and no other systemic or ocular diseases. A 12 mm horizontal single-line SS-OCT b-scan was performed to create a choroidal thickness (CT) profile. Validated automated segmentation and binarization were used in order to analyse choroidal, stromal, and vascular areas.

RESULTS

The percentage of choroidal vascularity (vascular area/total area) was 56.6% in KC patients vs. 49.4% in controls. Aged-adjusted choroidal, stromal, and vascular areas and corrected choroidal percentage of vascularity are statistically increased in KC patients when compared with healthy controls (p < 0.001). All these parameters show a decreasing trend with age. Both stromal and vascular areas were thicker in KC patients (p < 0.001).

CONCLUSIONS

Choroidal, stromal, and vascular areas and corrected choroidal percentage of vascularity are statistically increased in KC patients when compared with healthy controls. All these parameters tend to decrease with age.

Increased Choroidal Thickness in Keratoconus Patients: Perspectives in the Disease Pathophysiology

Purpose

To analyze and compare choroidal thickness between keratoconus (KC) patients and age-matched non-KC subjects.

Methods

A cross-sectional, case-control study. One hundred and thirty-four keratoconic eyes and 78 control eyes, from individuals aged from 12 to 30 years old, were studied. Patients with KC followed in Corneal Department of Centro Hospitalar São João, Porto, Portugal, were identified and consecutively included between December 2017 and February 2018. A spectral-domain optical coherence tomography (OCT) using depth enhanced imaging was performed, and choroidal thickness in the center of the fovea and at 500 μm intervals along a horizontal section was measured and compared.

Results

The statistical analysis showed that keratoconic eyes present a thicker choroid in every measured location (p < 0.05). Mean subfoveal choroidal thickness (SFCT) values obtained were 375.86 ± 89.29 and 322.91 ± 85.14 in keratoconus and control groups, respectively (p < 0.001). In a multivariate analysis, SFCT was significantly associated with spherical equivalent (p=0.004) and the presence of keratoconus (p < 0.001), but not with age (p=0.167), gender (p=0.579), or best-corrected visual acuity (p=0.178). In a "fixed model," keratoconus patients were found to have a 67.55 μm (95% CI 36.61-98.49) thicker subfoveal choroid compared to controls.

Conclusion

Keratoconus patients seem to have a thicker choroid than healthy individuals. The exact pathophysiological mechanism resulting in a thicker choroid in KC patients is not known, but it could possibly be associated with inflammatory choroidal mechanisms.

Matrix metalloproteinases in keratoconus - Too much of a good thing?

Keratoconus (KC) is a progressive, early onset, and often bilateral eye condition, in which the cornea gradually weakens and bulges out, and in advanced cases may eventually become cone-shaped. The available evidence suggests that it is a multifactorial disease with environmental and genetic contributions. Matrix Metalloproteinases (MMPs) are a family of 24 zinc-dependent proteases with the ability to degrade collagen and other extracellular matrix (ECM) proteins, which are important components of the cornea. During the past two decades a growing body of literature has accumulated suggesting a link between MMPs and keratoconus. This article aims to summarize the current knowledge on the role of MMPs in the pathogenesis of KC. MMP-driven ECM remodelling is thought to be a necessary step for cornea healing, but a fine balance in the expression of MMPs is essential in maintaining the integrity and transparency of the cornea and for its correct healing, and an imbalance in this tightly regulated process may, in the long term, result in the progressive weakening of the cornea. There is extensive evidence that MMPs are upregulated in the corneal tissue and tears of KC patients, implicating dysregulated proteolysis in KC, with an increase in the level of some MMPs, particularly MMP-1 and MMP-9, confirmed in multiple independent studies. There is also evidence for a causative link between inflammation, which could result from the mechanical trauma due to contact lens wearing or/and eye rubbing, and the increased MMPs production observed in KC. However, the precise role of each MMP in the cornea is still unclear and the mechanisms causing their upregulation are mostly undiscovered. Further studies are required to verify the functional role of specific MMPs in KC development and assess the genetic association between common MMPs variants and risk of KC. As MMPs inhibitors are in development, this information could potentially drive the discovery of new treatments for KC.