Tear Mediators in Corneal Ectatic Disorders

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.

Ocular surface inflammation and ectatic corneal disorders

PURPOSE OF REVIEW

Inflammatory mediators are a focus of recent corneal ectasia (CE) research and are a profound, modifiable contributor to CE in general and keratoconus (KC) in particular, opening a path to explore new methods of control. As advanced imaging technology and expanded population screening allow for earlier detection, the possibility of early intervention can profoundly change the prognosis of CE.

RECENT FINDINGS

Significant increases in the inflammatory mediators and immune components have been observed in the cornea, tear fluid, and blood of ectasia patients, while inflammation dampeners such as vitamin D and their receptors are reduced. Atopy and allergy have a strong association with KC, known to increase itch factors and stimulate eye rubbing, a risk factor in ectasia pathogenesis. Management of atopy or allergic conditions and topical anti-inflammatories has helped stabilize CE disease.

SUMMARY

Strategies such as monitoring inflammatory factors and using immune or inflammatory modulators, including managing subclinical inflammation, may be clinically beneficial in stabilizing the disease and improving outcomes. The detected factors are biomarkers, but as yet unproven to be sensitive or specific enough to be considered biomarkers for early detection of CE. The establishment of such biomarkers could improve the therapeutic outcome.

Keratoconus patients exhibit a distinct ocular surface immune cell and inflammatory profile

Inflammatory factors have been considered to contribute to keratoconus (KC) pathogenesis. This study aims to determine the immune cells subsets and soluble inflammatory factor profile on the ocular surface of KC patients. 32 KC subjects (51 eyes) across different grades of severity and 15 healthy controls (23 eyes) were included in the study. Keratometry and pachymetry measurements were recorded. Ocular surface immune cells (collected by ocular surface wash) immunophenotyped using flow cytometry include leukocytes, neutrophils, macrophages, natural killer (NK) cells, pan-T cells, gamma delta T (γδT) cells and NKT cells. Tear fluid collected using Schirmer's strip was used to measure 50 soluble factors by multiplex ELISA. Proportions of activated neutrophils, NK cells and γδT cells were significantly increased in KC patients. Significantly higher levels of tear fluid IL-1β, IL-6, LIF, IL-17A, TNFα, IFNα/β/γ, EPO, TGFβ1, PDGF-BB, sVCAM, sL-selectin, granzyme-B, perforin, MMP2, sFasL and IgE, along with significantly lower levels of IL-1α and IL-9 were observed in KC patients. Alterations observed in few of the immuno-inflammatory parameters correlated with grades of disease, allergy, eye rubbing and keratometry or pachymetry measurements. The observation implies a distinct immuno-inflammatory component in KC pathogenesis and its potential as an additional therapeutic target in KC management.

Tear Levels of Inflammatory Cytokines in Keratoconus: A Meta-Analysis of Case-Control and Cross-Sectional Studies

Purpose

To assess the tear levels of inflammatory cytokines in patients with keratoconus (KC).

Design

Systemic review and meta-analysis.

Methods

The following electronic databases and search engine were searched: PubMed, EMBASE, Web of Science, and Google Scholar. A systematic search of all relevant studies published through January 2021 was conducted, and the standardized mean difference (SMD) and 95% confidence interval (CI) of cytokine levels were calculated to estimate the pooled effects. Sensitivity analysis, subgroup analysis, and metaregression were applied to explore the sources of heterogeneity.

Results

A total of 7 studies with 374 participants (374 eyes) from clinical studies were included. The tear levels of interleukin-1 beta (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-α) were significantly increased in KC compared with normal controls. The SMD of IL-1β was 1.93 (95% CI 0.22 to 3.65, P = 0.03). The SMD of IL-6 was 1.22 (95% CI 0.59 to 1.84, P < 0.001). The SMD of TNF-α was 1.75 (95% CI 0.66 to 2.83, P = 0.002). There was no significant difference between the two groups on interleukin-4 (IL-4) and interleukin-10 (IL-10). The SMD for IL-4 was 2.36 (95% CI -0.28 to 5.00, P = 0.08) and for IL-10 was 0.30 (95% CI -1.29 to 1.89, P = 0.71). Meta-regression analysis indicated that the heterogeneity maybe significantly correlated with the method of detection, the different ages, and the source of population.

Conclusions

Our meta-analysis demonstrated that proinflammatory cytokines IL-1β, IL-6, and TNF-α were increased, indicating that cytokine profile changed in KC tears and inflammation may play an important role in the pathogenesis and development of KC.

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.

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.

Cytokine and Chemokine Concentration in the Tear of Patients with Age-Related Cataract

PURPOSE

The present study measured 41 soluble mediators in the tear of 19 patients with age-related cataract and 32 healthy adults as controls.

MATERIALS AND METHODS

This was a prospective, case-control study in which, using multiple immunoassays, we measured in tear samples the following molecules: EGF, FGF-2, Eotaxin, TGF-α, G-CSF, Flt-3L, GM-CSF, Fractalkine, IFN-α2, IFN-γ, GRO, IL-10, MCP-3, IL-12p40, MDC, IL-12p70, PDGF-AA, IL-13, PDGF-AB/BB, IL-15, sCD40L, IL-17a, IL-1ra, IL-1α, IL-9, IL-1β, IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, IL-8, IP-10, MCP-1, MIP-1α, MIP-1β, RANTES, TNFα, TNFβ, VEGF. Statistical analyses were done by multiple adjusted models and p values were corrected by the Benjamini and Hochberg method.

RESULTS

We did not find significant differences in the amount of the tested molecules in the tear fluid between cataract patients and controls. Correlation analyses relative to age were carried out for both groups. Analysis of MCP-1 tear levels revealed a direct correlation with age for normal healthy controls as well as for cataract patients. But IL-6 tear levels correlated with age only in the group of cataract patients. In addition, IL1-ra tear levels correlated with cataract nuclear grade; higher grades were associated with higher IL-1ra concentrations.

CONCLUSIONS

Our results suggest that ocular aging is accompanied by increased production of IL-6 and MCP-1, which can be measured in tear fluid.

ABBREVIATIONS

AMD: Age-Related Macular Degeneration; EGF: Epidermal growth factor; Eotaxin: Eosinophil chemotactic proteins; FasL: Fas ligand; FGF-2: Basic fibroblast growth factor 2; Flt-3L: Fms related tyrosine kinase 3 ligand; G-CSF: Granulocyte colony stimulating factor; GM-CSF: Granulocyte macrophage colony stimulating factor; GRO: Growth regulated protein; HGF: Human growth factor; ICAM-1: Intercellular adhesion molecule-1; IFNα2: Interferon alpha 2; IFNγ: Interferon gamma; IL: Interleukin; IL-1ra: Interleukin-1 receptor antagonist; IL-12p40: Interleukin-12 subunit p40; IL-12p70: Interleukin-12 subunit p70; IP-10: Interferon gamma-induced protein 10; MCP-1: Monocyte chemotactic protein 1; MCP-3: Monocyte chemotactic protein 3; MDC: Macrophage derived chemokine; MIG: Monokine induced by gamma interferon; MIP-1α: Macrophage inflammatory proteins 1 alpha; MIP-1β: Macrophage inflammatory proteins 1 beta; MMPs: Matrix metalloproteinases; MMP-9: Matrix metalloproteinase 9; PAI1: Plasminogen activator inhibitor 1; PDGF-AA: Platelet-derived growth factor subunit AA; PDGF-AB/BB: Platelet-derived growth factor subunit AB and BB; PIGF: Placenta growth factor; RANTES: Regulated on activation, normal T cell expressed and secreted; SAA: Serum amyloid A; sCD40L: Soluble CD40 ligand; sTNF-RII: Soluble tumor necrosis factor receptor; TBUT Tear breakup time; TGF-α: Transforming growth factor alpha; TGF-β: Transforming growth factor beta; TNFα: Tumor necrosis factor alpha; TNFβ: Tumor necrosis factor beta; VCAM: Vascular cell adhesion molecule; VEGF: Vascular endothelium growth factor.

Collagen cross-linking impact on keratoconus extracellular matrix

Background

Keratoconus (KC) is a common multifactorial ectatic corneal disease with unknown onset. KC most commonly appears in adolescence and affects approximately 1:400 people worldwide. Treatment options, for advanced KC cases, are collagen cross-linking (CXL) and corneal transplants. CXL is a new KC treatment that helps arrest the disease. Unfortunately, only a fraction of KC patients will qualify for CXL treatment. Our goal, in this study, was to begin to understand how CXL affects the corneal microenvironment and pave the way towards a more patient-driven CXL treatment.

Methods

Primary human corneal fibroblasts from healthy and KC donors were plated on transwell polycarbonate membranes and stimulated by a stable vitamin C. At 4 weeks, riboflavin was added followed by UVA irradiation. Transmission Electron Microscopy (TEM) and western blots were used to assess the effect of CXL on the extracellular matrix (ECM) and the resident cells, pre- and post CXL.

Results

Data shows CXL improved lamellar organization showing more organized collagen fibrils decorated with proteoglycans (PGs). The distribution of the collagen fibrils and interfibrillar spacing was also visibly improved, post-CXL. Lumican, mimecan, and decorin were the dominant PGs and were significantly upregulated in post-CXL cultures. ECM degradation proteins, matrix metalloproteinases (MMPs), MMP-1, -3, and -9, but not MMP-2, were significantly downregulated post-CXL. TIMP-1 and -2 were not modulated by CXL.

Conclusion

The unknown effects of CXL on the human corneal microenvironment have hampered our ability to make CXL available to all KC patients. Our current study provides a deeper understanding on CXL activity, using our unique 3D in vitro model.

Macular Choroidal Thickening in Keratoconus Patients: Swept-Source Optical Coherence Tomography Study

Purpose

To determine the choroidal thickness (CT) profile in keratoconus (KC) patients using swept-source optical coherence tomography (SS-OCT).

Methods

This was a prospective, cross-sectional study. One hundred two eyes of 52 KC patients were studied using Pentacam and SS-OCT. The macular CT profile was created by manually measuring the distance between the retinal pigment epithelium and the choroid-sclera junction on horizontal b-scans at nine different macular locations. The results were compared to 93 eyes of 93 healthy controls.

Results

Mean age of the KC group was 34.9 ± 13.5 years and mean axial length (AL) was 24.1 ± 1.3 mm. Mean topographic KC classification (TKC) was 2.0; 39 eyes were classified as early KC (TKC <1–2), 34 eyes as moderate (TKC 2, 2–3), and 29 as advanced (TKC 3+). Mean subfoveal CT was 383.2 μm in KC patients and 280.5 μm in control group (P < 0.001). CT in KC patients was statistically thicker in all measure locations (P < 0.001). CT in KC eyes decreased with age, approaching control group at >45 years old, losing statistical significance (P = 0.37).

Conclusions

CT in KC patients is statistically thicker than in healthy population. After age 45, CT decreases approaching control group values.

Translational Relevance

This study describes changes in the CT profile of KC patients, a disease that was considered purely corneal. These choroidal changes argue that KC is a disease that likely involves several ocular structures other than the cornea, and could open new research lines related to the pathophysiology of KC.

Tear Martix Metalloproteinase-9 and Tissue Inhibitor of Metalloproteinase-1 in Post-Lasik Ectasia

PURPOSE

To estimate the concentrations of matrix metalloproteinase-9 (MMP-9) and tissue inhibitors of metalloproteinase-1 (TIMP-1) in the tear film of cases with post-Lasik ectasia (PLE) to spot any role of these mediators.

SETTINGS

Ophthalmology department, Benha University hospitals, Egypt.

METHODS

Twelve eyes of 12 patients with PLE, 30 eyes of 30 patients with KC, 25 eyes of 25 subjects with uncomplicated Lasik and finally 25 eyes of 25 healthy subjects as a control group were studied. Subjects with ocular surface diseases, previous ocular surgeries except for Lasik in PLE group and Lasik group, were excluded. All subjects had full ophthalmic examination and Pentacam imaging. The concentration of tear MMP-9 and TIMP-1 was measured by ELISA.

RESULTS

Our results showed a significant elevation in the level of MMP-9 and a significant reduction in the level of TIMP-1 in tear samples from PLE cases (MMP-9 was 59.17 ± 28.15 ng/ml, and TIMP-1 was 110.3 ± 50.6 ng/ml) and also in KC cases (MMP-9 was 53.12 ± 17.35 ng/ml, and TIMP-1 was 105.8 ± 56.3 ng/ml) when compared to post-Lasik group (MMP-9 was 35.65 ± 17.32 ng/ml, and TIMP-1 was 155.2 ± 39.4 ng/ml) and control group (MMP-9 was 31.92 ± 20.78 ng/ml, and TIMP-1 was 162.5 ± 48.2 ng/ml).

CONCLUSION

The results pointed to potential role of MMP-9 in the pathogenesis of PLE and also referred to a biochemical similarity between PLE and KC. More studies are needed in the future to investigate larger number of tear mediators.

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

Inflammation may play a significant role in Keratoconus (KC), but the implication of immunity on this inflammatory response is unknown. Therefore, our aim was to determine the expression levels of Toll-like receptors 2 (TLR2) and 4 (TLR4) in monocytes and neutrophils from patients with KC and control subjects for demonstrating the role of innate immunity in KC. We also study the correlation between TLR2/TLR4 expression and serum levels of proinflammatory markers (IL-1β, IL-6, TNF-α, MMP-9 and NF-κB). Forty patients with bilateral KC (55% males; mean age; 33.1 ± 10.9 years) and 20 control subjects (55% males; mean age; 30.4 ± 7.6 years) were included in the study. Our results showed that mean expression of TLR2 and TLR4 in both neutrophils and monocytes was significantly higher in patients with KC compared to control subjects (all p < 0.0001). Furthermore, KC patients also showed higher serum levels of IL-1B, IL-6, TNF-α, MMP-9 (all p < 0.0001) and NF-κB (p = 0.036). In addition, we found a strong correlation between TLR2 expression in both monocytes and neutrophils (all p < 0.0001), and TLR4 in monocytes (all p < 0.05) with serum levels of IL-1B, IL-6, TNF-α and MMP-9. In conclusion, these findings suggest that TLRs may play an important role in the pathophysiology of KC.