Intra- and inter-day variation of cytokines and chemokines in tears of healthy subjects

Tear-Based Ocular Wearable Biosensors for Human Health Monitoring

Wearable tear-based biosensors have garnered substantial interest for real time monitoring with an emphasis on personalized health care. These biosensors utilize major tear biomarkers such as proteins, lipids, metabolites, and electrolytes for the detection and recording of stable biological signals in a non-invasive manner. The present comprehensive review delves deep into the tear composition along with potential biomarkers that can identify, monitor, and predict certain ocular diseases such as dry eye disease, conjunctivitis, eye-related infections, as well as diabetes mellitus. Recent technologies in tear-based wearable point-of-care medical devices, specifically the state-of-the-art and prospects of glucose, pH, lactate, protein, lipid, and electrolyte sensing from tear are discussed. Finally, the review addresses the existing challenges associated with the widespread application of tear-based sensors, which will pave the way for advanced scientific research and development of such non-invasive health monitoring devices.

Tear levels of Transforming Growth Factor-β1 and Interleukin 1-β, and clinical correlations in new contact lens users

PURPOSE

To assess alterations in the tear Transforming Growth Factor (TGF)-β1 and Interleukin (IL1)-β concentration in new contact lens wearers; and explore correlations with tear film stability, and ocular physiological response.

METHODS

In this clinical setting, 12 neophytes (5 males), with an average age of 24.0 ± 5.0 years were fitted with delefilcon A contact lenses. Physiological responses (bulbar and limbal hyperemia), Pre-corneal (NIBUT), Pre-lens (PL-NIBUT) non-Invasive Break-Up Times, and tear samples were collected in the morning (before lens insertion; 9 - 10 a.m.) and afternoon (before lens removal; 7 - 8p.m.) of the same day. NIBUT and PL-NIBUT were measured using a tearscope. Tear samples were assayed for TGF-β1 and IL1-β concentrations using Enzyme-Linked Immunosorbent Assay kits. An 11-members control group (6 males) aged 25.0 ± 5.0, served to assess biomarker levels in non-contact lens wearers' tears.

RESULTS

Subjects wore lenses for an average of 7 h and 20 min (range: 6 to 9 h). Bulbar and limbal hyperemia increased significantly throughout the day (p < 0.001). PL-NIBUT were lower than NIBUT (4.7 ± 2.0 Vs. 12.2 ± 8.8 s; p < 0.001). The IL1-β levels were higher in neophytes than controls (3.2 ± 4.7 Vs. 0.1 ± 0.1 pg/ml; p = 0.05), correlating significantly with bulbar (r = 0.405, p = 0.008) and limbal hyperemia (r = 0.499, p = 0.027). No substantial changes were reported for TGF-β1.

CONCLUSION

The presence of TGF-β1 in tears does not appear significantly affected by lens wear. The association between physiological parameters and IL1-β levels suggests that lenses may disrupt ocular surface homeostasis by altering cytokine regulatory mechanisms. However, due to its low concentration, IL1-β's role in the subclinical inflammatory response to lens wear is limited.

Importance of Circadian Rhythms in the Ocular Surface

Circadian rhythms are a ubiquitous feature throughout the organism. Accumulating evidence suggests that the dysfunction of circadian rhythms due to genetic mutations or environmental factors contributes to the genesis and progress of multiple diseases. The physiological homeostasis of the ocular surface, like any other tissue or organ, is also orchestrated by circadian rhythms. In this review, we summarize the molecular clocks and the expression of clock-controlled genes in the mammalian ocular surface. Based on the circadian expression of these genes, we conclude the diurnal oscillations of cellular biological activities in the mammalian ocular surface. Moreover, we evaluate the factors entraining circadian oscillators in the ocular surface. Finally, we further discuss the latest development of the close correlation between circadian rhythms and ocular health. Briefly, this review aimed to synthesize the previous studies to aid in understanding the importance of circadian rhythms in the ocular surface and the possible opportunities for circadian rhythm-based interventional strategies to restore the homeostasis of the ocular surface.

Tear Fluid Progranulin as a Noninvasive Biomarker for the Monitoring of Corneal Innervation Changes in Patients With Type 2 Diabetes Mellitus

Purpose

This study aimed to investigate the expression levels of progranulin (PGRN) in the tears of patients with diabetic retinopathy (DR) versus healthy controls. Additionally, we sought to explore the correlation between PGRN levels and the severity of ocular surface complications in patients with diabetes.

Methods

In this prospective, single-visit, cross-sectional study, patients with DR (n = 48) and age-matched healthy controls (n = 22) were included and underwent dry eye examinations. Tear fluid was collected, and its components were analyzed using the Luminex assay. The subbasal nerve plexus of all participants was evaluated by in vivo confocal microscopy.

Results

Patients with DR exhibited more severe dry eye symptoms, along with a reduction in nerve fiber density, length, and branch density within the subbasal nerve plexus, accompanied by an increase in the number of dendritic cells. Tear PGRN levels were also significantly lower in patients with diabetes than in normal controls, and the levels of some inflammatory factors (TNF-α, IL-6, and MMP-9) were higher in patients with DR. Remarkably, the PGRN level significantly correlated with nerve fiber density (R = 0.48, P < 0.001), nerve fiber length (R = 0.65, P < 0.001), and nerve branch density (R = 0.69, P < 0.001).

Conclusions

Tear PGRN levels might reflect morphological changes in the corneal nerve plexus under diabetic conditions, suggesting that PGRN itself is a reliable indicator for predicting the advancement of neurotrophic keratopathy in patients with diabetes.

Translational Relevance

PGRN insufficiency on the ocular surface under diabetic conditions was found to be closely associated with nerve impairment, providing a novel perspective to discover the pathogenesis of diabetic complications, which could help in developing innovative therapeutic strategies.

Multiplatform tear proteomic profiling reveals novel non-invasive biomarkers for diabetic retinopathy

OBJECTIVES

To investigate a comprehensive proteomic profile of the tear fluid in patients with diabetic retinopathy (DR) and further define non-invasive biomarkers.

METHODS

A cross-sectional, multicentre study that includes 46 patients with DR, 28 patients with diabetes mellitus (DM), and 30 healthy controls (HC). Tear samples were collected with Schirmer strips. As for the discovery set, data-independent acquisition mass spectrometry was used to characterize the tear proteomic profile. Differentially expressed proteins between groups were identified, with gene ontology enrichment analysis and Kyoto Encyclopedia of Genes and Genomes enrichment analysis further developed. Classifying performance of biomarkers for distinguishing DR from DM was compared by the combination of three machine-learning algorithms. The selected biomarker panel was tested in the validation cohort using parallel reaction monitoring mass spectrometry.

RESULTS

Among 3364 proteins quantified, 235 and 88 differentially expressed proteins were identified for DR when compared to HC and DM, respectively, which were fundamentally related to retina homeostasis, inflammation and immunity, oxidative stress, angiogenesis and coagulation, metabolism, and cellular adhesion processes. The biomarker panel consisting of NAD-dependent protein deacetylase sirtuin-2 (SIR2), amine oxidase [flavin-containing] B (AOFB), and U8 snoRNA-decapping enzyme (NUD16) exhibited the best diagnostic performance in discriminating DR from DM, with AUCs of 0.933 and 0.881 in the discovery and validation set, respectively.

CONCLUSIONS

Tear protein dysregulation is comprehensively revealed to be associated with DR onset. The combination of tear SIR2, AOFB, and NUD16 can be a novel potential approach for non-invasive detection or pre-screening of DR.

CLINICAL TRIAL REGISTRATION

Chinese Clinical Trial Registry Identifier: ChiCTR2100054263. https://www.chictr.org.cn/showproj.html?proj=143177 . Date of registration: 2021/12/12.

Tear biomarkers

An extensive exploration of lacrimal fluid molecular biomarkers in understanding and diagnosing a spectrum of ocular and systemic diseases is presented. The chapter provides an overview of lacrimal fluid composition, elucidating the roles of proteins, lipids, metabolites, and nucleic acids within the tear film. Pooled versus single-tear analysis is discussed to underline the benefits and challenges associated with both approaches, offering insights into optimal strategies for tear sample analysis. Subsequently, an in-depth analysis of tear collection methods is presented, with a focus on Schirmer's test strips and microcapillary tubes methods. Alternative tear collection techniques are also explored, shedding light on their applicability and advantages. Variability factors, including age, sex, and diurnal fluctuations, are examined in the context of their impact on tear biomarker analysis. The main body of the chapter is dedicated to discussing specific biomarkers associated with ocular discomfort and a wide array of ocular diseases. From dry eye disease and thyroid-associated ophthalmopathy to keratoconus, age-related macular degeneration, diabetic retinopathy, and glaucoma, the intricate relationship between molecular biomarkers and these conditions is thoroughly dissected. Expanding beyond ocular pathologies, the chapter explores the applicability of tear biomarkers in diagnosing systemic diseases such as multiple sclerosis, amyotrophic lateral sclerosis, Alzheimer's disease, Parkinson's disease, and cancer. This broader perspective underscores the potential of lacrimal fluid analysis in offering non-invasive diagnostic tools for conditions with far-reaching implications.

Heritability of tear fluid cytokines in healthy twins

PURPOSE

Ocular surface disease is common and it is associated with elevated concentration levels of cytokines in tear fluid. Studies of the normal variation in tear fluid inflammatory markers are lacking. New knowledge may help guide research into ocular surface disease biomarkers and therapeutics.

METHODS

In this prospective twin cohort study, healthy individuals were recruited from a population-based registry. Tear fluid was collected with the Schirmer test strips was submerged in phosphate buffered saline and stored at -80° before undergoing 27-cytokine multiplex immunoassay analysis. Broad-sense heritability (h2) of cytokine concentrations was analyzed.

RESULTS

90 participants (23 monozygotic and 22 dizygotic twin pairs) were included. Data availability allowed for heritability analysis of 15 cytokines, and a h2 >50% was seen for 10 cytokines. A statistical power of >80% was achieved for heritability analyses of the cytokines interferon gamma induced protein 10 (h2 = 94.8%), eotaxin (89.8%), interleukin 7 (86.6%), interleukin 1β (82.2%) and monocyte chemoattractant protein 1 (68.2%).

CONCLUSIONS

The tear fluid concentration of several analyzed cytokines was found to be highly heritable. A considerable amount of the inter-individual variation observed for the concentration of certain tear fluid cytokines can be linked to hereditary factors that cannot easily be modified by changing factors in the environment of patients. This suggests that a higher success in ocular surface disease drug discovery may be anticipated for drugs that have targets in specific populations, and points to the importance of emphasizing known preventive measures of ocular surface disease and examinations of close relatives of patients with ocular surface disease, such as dry eye disease.

Unraveling the Intraday Variations in the Tear Fluid Proteome

Purpose

Tear fluid is a complex and dynamic biological fluid that plays essential roles in maintaining ocular homeostasis and protecting against the external environment. Owing to the small sample volume, studying the tear proteome is challenging. However, advances in high-resolution mass spectrometry have expanded tear proteome profiling, revealing >500 unique proteins. Tears are emerging as a noninvasive source of biomarkers for both ocular and systemic diseases; nevertheless, intraday variability of proteins in tear fluid remains questionable. This study investigates intraday variations in the tear fluid proteome to identify stable proteins that could act as candidate biomarkers.

Methods

Tear samples from 15 individuals at four time points (10 am, 12 pm, 2 pm, and 4 pm) were analyzed using mass spectrometry to evaluate protein variation during these intervals. Technical variation was assessed by analyzing pooled samples and was subtracted from the total variation to isolate biological variability.

Results

Owing to high technical variation, low-abundant proteins were filtered, and only 115 proteins met the criteria for further analysis. These criteria include being detected at all four time points in at least eight subjects, having a mean peptide-spectrum match count greater than 5, and having a technical variation less than 0.10. Lactotransferrin, lipocalin-1, and several immunoglobulins were among the 51 stable proteins (mean biological coefficient of variation < 0.10). Additionally, 43 proteins displayed significant slopes across the 4 time points, with 17 increasing and 26 decreasing over time.

Conclusions

These findings contribute to the understanding of tear fluid dynamics and further expand our knowledge of the tear proteome.

Association of Tear Cytokine Ratios with Symptoms and Signs of Dry Eye Disease: Biomarker Data from the Dry Eye Assessment and Management Study

PURPOSE

To assess the relationship between tear inflammatory cytokine ratios (CRs) and signs and symptoms of dry eye disease (DED) to investigate the possible use of tear CRs, which may better address the complexity of cytokine interactions than absolute cytokine levels, as a DED biomarker.

METHODS

Tear concentrations of IL-1b, IL-6, IL-8, IL-10, IL-17A, IFN-g, and TNF-a were measured using standardized procedures, as were DED signs (corneal and conjunctival staining scores, tear break-up time, Schirmer test, Meibomian gland plugging, tear osmolarity, composite sign severity score) and symptoms [Ocular Surface Disease Index (OSDI)]. Ratios between pro-inflammatory (IL-1b, IL-8, IL-17A, IFN-g, and TNF-a) and anti-inflammatory (IL-10) cytokines were calculated. Given its opposing roles in inflammation, IL-6 was tested as both a pro- and anti-inflammatory cytokine. Correlations between CR and DED symptoms and signs were calculated using Spearman correlation coefficients (rho).

RESULTS

At baseline, 131 patients, 80.2% female and mean age 54.2 years (SD 14.1, range 20-82), from 10 sites of the Dry Eye Assessment and Management study had sufficient tear volumes ≥4 μL for analysis. IL-6:IL-10, IL-8:IL-10, and TNF-a:IL-10 had some significant correlations, mostly with conjunctival or corneal staining or the composite sign severity score (IL-8:IL-10 and conjunctival staining: rho = 0.19, p = 0.03; IL-6:IL-10 and corneal staining: rho = 0.31, p < 0.001; IL-8:IL-10 and corneal staining: rho = 0.21, p = 0.01; IL-6:IL-10 and composite sign severity score: rho = 0.26, p = 0.003; IL-8:IL-10 and composite sign severity score: rho = 0.26, p = 0.003; TNF-a:IL-10 and corneal staining: rho = 0.29, p < 0.001; TNF-a:IL-10 and Schirmer test: rho = -0.23, p = 0.009). CRs had no significant correlation with DED symptoms. All significant correlations using IL-6 in the denominator (anti-inflammatory) produced counterintuitive results based on clinical understanding of the disease.

CONCLUSIONS

Pro- to anti-inflammatory CR was weakly correlated with some DED signs and not with symptoms, as measured by OSDI. Future studies in different dry eye populations are needed and should address sampling biases and tear collection techniques.

Efficacy of Interleukin-1β Inhibitor on Dry Eye Disease in Patients with Degenerative Arthritis

Purpose

To evaluate diacerein (interleukin-1β inhibitor) efficacy on ocular surface disease (OSD).

Patients and Methods

This prospective observational study included patients who received diacerein for osteoarthritis and had dry eye (DE). The primary outcome was corneal staining score. Secondary outcomes were ocular surface disease index (OSDI) score, tear breakup time (TBUT), tear osmolarity (Osm), Schirmer's test results, interleukin-1α (IL-1α), interleukin-1β (IL-1β), and interleukin-1 receptor antagonist (IL-1Ra) levels in tears. All measurements were done at baseline and 2-month follow-up visits. Linear mixed models were used to examine the effect of all parameters, and log-transformed models were used for IL-1α, IL-1β, and IL-1Ra analyses.

Results

Thirty-four patients (31 females and 3 males) were enrolled. The corneal staining score improved by 1.29 points (P=0.022, 95% confidence interval [95% CI] 0.19 to 2.40) after 2 months, and the OSDI score improved by 17.2 points (P<0.001, 95% CI 10.82 to 23.58) but TUBT decreased by 0.66 seconds (P=0.021, 95% CI 0.10 to 1.22). No significant differences were observed in the tear Osm and Schirmer's test. IL-1Ra demonstrated no statistical difference, IL-1α was significantly increased by 80% (P=0.260), and IL-1β was significantly decreased by 99.21% (P<0.001).

Conclusion

Diacerein can improve corneal staining and decrease IL-1β levels in tears, which reflects better DE symptoms. Diacerein may be a promising alternative treatment for patients with OSD and osteoarthritis.

Investigation of Inter- and Intra-Day Variability of Tear Fluid Regarding Flow Rate, Protein Concentration as well as Protein Composition

Purpose

The purpose of this study was to present the determination of inter- and intra-day variations in tear flow rate, and tear fluid protein concentration, as well as protein composition regarding their impact for future biomarker studies.

Methods

Tear fluid was collected noninvasively from 18 healthy subjects by performing Schirmer tests at 4 different time points repetitive in a period of 2 days. The tear flow rate on the Schirmer test strips was measured. Proteins were extracted from strips and quantified using amino acid analysis. Protein composition was analyzed by the strips data-independent (DIA) based mass spectrometry. To exclude any impairments to health, volunteers underwent a detailed neurological as well as an ophthalmological examination.

Results

Whether tear fluid was collected from oculus sinister or oculus dexter did not affect the tear flow rate (P ≈ 0.63) or protein concentration (P ≈ 0.97) of individual subjects. Moreover, protein concentration was independent from the tear volume, so that a change in volume may only influence the total protein amount. When the examination days were compared, investigation of tear flow rate (P ≈ 0.001) and protein concentration (P ≈ 0.0003) indicated significant differences. Further, mass spectrometric analysis of tear fluid revealed 11 differentially regulated proteins when comparing both examination days.

Conclusions

Our findings provide evidence of inter-day variation in tear flow rate, tear proteome concentration, and composition in healthy subjects, suggesting that inter-day variation needs to be taken into consideration in biomarker research of tear fluid. Identified proteins were assigned to functions in the immune response, oxidative and reducing processes, as well as mannose metabolism.

Gene expression signatures in conjunctival fornix aspirates of patients with dry eye disease associated with Meibomian gland dysfunction. A proof-of-concept study

BACKGROUND

Meibomian gland dysfunction (MGD) is one of the most common conditions in ophthalmic practice and the most frequent cause of evaporative dry eye disease (DED). However, the immune mechanisms leading to this pathology are not fully understood and the diagnostic tests available are limited. Here, we used the nCounter technology to analyze immune gene expression in DED-MGD that can be used for developing diagnostic signatures for DED.

METHODS

Conjunctival cell samples were obtained by aspiration from patients with DED-MGD (n = 27) and asymptomatic controls (n = 22). RNA was purified, converted to cDNA, preamplified and analyzed using the Gene Expression Human Immune V2 panel (NanoString), which includes 579 target and 15 housekeeping genes. A machine learning (ML) algorithm was applied to design a signature associated with DED-MGD.

RESULTS

Forty-five immune genes were found upregulated in DED-MGD vs. controls, involved in eight signaling pathways, IFN I/II, MHC class I/II, immunometabolism, B cell receptor, T Cell receptor, and T helper-17 (Th-17) differentiation. Additionally, statistically significant correlations were found between 31 genes and clinical characteristics of the disease such as lid margin or tear osmolarity (Pearson's r < 0.05). ML analysis using a recursive feature elimination (RFE) algorithm selected a 4-gene mRNA signature that discriminated DED-MGD from control samples with an area under the ROC curve (AUC ROC) of 0.86 and an accuracy of 77.5%.

CONCLUSIONS

Multiplexed mRNA analysis of conjunctival cells can be used to analyze immune gene expression patterns in patients with DED-MGD and to generate diagnostic signatures.

The cGAS-STING pathway-dependent sensing of mitochondrial DNA mediates ocular surface inflammation

The innate immune response is the main pathophysiological process of ocular surface diseases exposed to multiple environmental stresses. The epithelium is central to the innate immune response, but whether and how innate immunity is initiated by ocular epithelial cells in response to various environmental stresses in ocular surface diseases, such as dry eye, is still unclear. By utilizing two classic experimental dry eye models-a mouse ocular surface treated with benzalkonium chloride (BAC) and a mouse model with surgically removed extraorbital lachrymal glands, as well as dry eye patient samples-along with human corneal epithelial cells (HCE) exposed to hyperosmolarity, we have discovered a novel innate immune pathway in ocular surface epithelial cells. Under stress, mitochondrial DNA (mtDNA) was released into the cytoplasm through the mitochondrial permeability transition pore (mPTP) and further activated the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway, aggravating downstream inflammatory responses and ocular surface damage. Genetic deletion or pharmacological suppression of STING and inhibition of mtDNA release reduced inflammatory responses, whereas mtDNA transfection supported cytoplasmic mtDNA-induced inflammatory responses by activating the cGAS-STING pathway. Our study clarified the cGAS-STING pathway-dependent sensing of mitochondrial DNA-mediated ocular surface inflammation, which elucidated a new mechanism of ocular surface diseases in response to multiple environmental stresses.

Tear Biomarkers and Alzheimer's Disease

Alzheimer's disease (AD) is an age-related progressive neurodegenerative brain disorder that represents the most common type of dementia. It poses a significant diagnostic challenge that requires timely recognition and treatment. Currently, there is no effective therapy for AD; however, certain medications may slow down its progression. The discovery of AD biomarkers, namely, magnetic resonance imaging, positron emission tomography and cerebrospinal fluid molecules (amyloid-β and tau) has advanced our understanding of this disease and has been crucial for identifying early neuropathologic changes prior to clinical changes and cognitive decline. The close interrelationship between the eye and the brain suggests that tears could be an interesting source of biomarkers for AD; however, studies in this area are limited. The identification of biomarkers in tears will enable the development of cost-effective, non-invasive methods of screening, diagnosis and disease monitoring. In order to use tears as a standard method for early and non-invasive diagnosis of AD, future studies need to be conducted on a larger scale.

Tear Cytokine Levels in Sicca Syndrome-Related Dry Eye: A Meta-Analysis

Sjogren's syndrome (SS) is an autoimmune disease that affects exocrine glands, mainly salivary and lacrimal glands. Several studies have investigated cytokine profiles in tears in order to understand the pathogenesis of SS and find additional diagnostic markers. This systematic review and meta-analysis aimed to analyze cytokines in tears of SS patients. A systematic literature search of the Cochrane, Medline via PubMed, Scopus, and Web of Science databases was conducted using key terms related to "Sjögren's syndrome" and "tears" combined with "biomarker", "cytokines", "interleukin", and "chemokines", following PRISMA guidelines. Article selection was subjected to certain eligibility criteria. A total of 17 articles (from 1998 and 2022) were selected for the quantitative and qualitative analysis. When compared to controls, concentrations of IFN-γ, TNF-α, IL-1α, IL-1 Ra, IL-4, IL-6, IL-8, IL-10, IL-17, IL-21 and IL-22 were consistently higher; however, IL-23 was significantly lower in patients with SS compared to the controls. Tear levels of some cytokines were significantly elevated among SS groups compared to control groups. Therefore, these cytokines could be potential biomarkers of SS. However, standardization of sample collection and analytical methods is necessary in order to translate these findings into clinical practice.

Tear Fluid Biomarkers and Quality of Life in People with Type 2 Diabetes and Dry Eye Disease

Dry eye disease (DED) can be extremely distressing and is common in type 2 diabetes (T2D). To investigate potential biomarkers of DED in T2D, panels of proteins in tears, alongside clinical signs and symptoms of DED, were assessed. Patients were classified into four groups: T2D + DED (n = 47), T2D-only (n = 41), DED-only (n = 17) and healthy controls (n = 17). All patients underwent the Ocular Surface Disease Index (OSDI) and Dry Eye-Related Quality of Life (DEQS) questionnaires, tear evaporation rate (TER), fluorescein tear break-up time (fTBUT), corneal fluorescein staining (CFS) and Schirmer 1 test assessments. Six metabolic proteins and 14 inflammatory cytokines were analyzed with multiplex bead analysis. Interleukin (IL)-6 and IL-8 concentrations in tears were significantly higher in the T2D + DED group, and these biomarkers were positively correlated with CFS. In addition, tear IL-6 was negatively correlated with fTBUT in the T2D + DED group. Clinical signs of DED in the T2D + DED group were similar to the DED-only group. The T2D + DED group had more patients with moderate and severe DED (versus the DED-only group), suggesting a different pathogenesis for DED in T2D versus DED-only. Therefore, IL-6 and IL-8 could potentially be diagnostic biomarkers of DED in T2D.

The genetic polymorphisms and levels of adipokines and adipocytokines that influence the risk of developing gestational diabetes mellitus in Thai pregnant women

INTRODUCTION

Aberrant immune and inflammatory response is thought to be involved in the pathogenesis of gestational diabetes mellitus (GDM).

OBJECTIVE

To investigate the genetic polymorphisms and levels of adipokines/adipocytokines that influence the risk of developing GDM in Thai women.

RESEARCH DESIGN & METHODS

This case-control recruited 400 pregnant Thai women. A total of 12 gene polymorphisms at ADIPOQ, adipsin, lipocalin-2, PAI-1, resistin, IL-1β, IL-4, IL-17A, TGF-β, IL-10, IL-6, and TNF-α were analyzed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay and RNase H2 enzyme-based amplification (rhAmp) SNP assay. Serum levels of adipokines/adipocytokines were evaluated using Luminex assays.

RESULTS

Mean age, weight before and during pregnancy, body mass index before and during pregnancy, blood pressure, gestational age at blood collection, and median 50 g glucose challenge test were significantly higher in GDM women than control. Significantly lower adiponectin and higher IL-4 levels were found in GDM compared to controls (p = 0.001 and p = 0.03, respectively). The genotype frequencies of IL-17A (rs3819025) were significantly different between GDM and controls (p = 0.01). Using additive models, IL-17A (rs3819025) and. TNF-α (rs1800629) were found to be independently associated with increased risk of GDM (odds ratio [OR]: 2.867; 95 % confidence interval [CI]: 1.171-7.017; p = 0.021; and OR: 12.163; 95 %CI: 1.368-108.153; p = 0.025, respectively). In GDM with IL-17A (rs3819025), there was a significant negative correlation with lipocalin-2 and PAI-1 levels (p = 0.038 and p = 0.004, respectively).

CONCLUSION

The results of this study highlight the need for genetic testing to predict/prevent GDM, and the importance of evaluating adipokine/adipocytokine levels in Thai GDM women.

Association of Tear Cytokine Concentrations with Symptoms and Signs of Dry Eye Disease: Baseline Data from the Dry Eye Assessment and Management (DREAM) Study

PURPOSE

To describe tear concentrations of IL-1β, Il-6, IL-8, IL-10, IL-17A, IFNγ and TNFα in tears, collected by microcapillaries, and their correlation with symptoms and signs in subjects with dry eye disease (DED) in the DREAM Study.

METHODS

Cytokine levels of patients with moderate to severe DED were determined using a magnetic bead assay. Scores for Ocular Surface Disease Index, corneal and conjunctival staining, tear break-up time (TBUT), and Schirmer's test were obtained using standardized procedures. Associations of cytokines with each other and signs/symptoms were assessed with Spearman correlation coefficients (r).

RESULTS

Assay results from 131 patient samples from 10 sites with tear volumes ≥ 4 ul were analyzed. Cytokine concentrations did not correlate with each other in a generally acknowledged pro-inflammatory/anti-inflammatory pattern, such as proinflammatory IL-17A and IFNγ were not inversely correlated to anti-inflammatory cytokine IL-10, and cytokines did not correlate with DED symptoms. Lower corneal staining was correlated with higher concentrations of IL-17A (r= -0.24, p = 0.006), IL-10 (r= -0.25, p = 0.005) and IFNγ (r= -0.33, p = 0.0001). Higher concentrations of IFNγ were associated with lower conjunctival staining (r= -0.18, p = 0.03). Higher concentrations of IL-17A were associated with higher TBUT scores (r = 0.19 p = 0.02).

CONCLUSIONS

Cytokines IL-10, IL-17A and IFNγ were highly correlated with each other but weakly correlated with some DED signs. No key cytokines or definitive expression patterns were identified in this study of moderate to severe DED patients. Further studies addressing various biases, including methodological and sampling biases, and standardization of methodology for inter-laboratory consistency are needed to confirm and establish pathological and clinical relevance of tear cytokines in DED.

Tear levels of IL-7, IL-1α, and IL-1β may differentiate between IgG4-related disease and Sjögren's syndrome

We aim to assess and compare a cytokine and chemokine profile in tears from patients with IgG4-related disease (IgG4-RD) and Sjögren's syndrome (SS), and to see if this profile could aid in differentiating these two diseases. We included 10 patients with IgG4-RD who met the Comprehensive Diagnostic Criteria for IgG4-RD and 17 patients who met the AECG criteria for primary SS. The Schirmer-I test was carried out using two standardized sterile tear strips, which were then immediately frozen at - 86 °C until assayed. The tears were extracted from the strips after they had been defrosted using a buffer containing 0.5 M NaCl and 0.5% Tween-20. The amounts (pg/ml) of the following cytokines and chemokines were then measured using luminometry: IFN-γ, TNF-α, G-CSF, IL-1-α, IL-1β, IL-4, IL-7, IL-12p40, IL-12p70, IL-13, IL-17A, CCL2, CCL3, CCL4, CCL11, and CXCL10. In the IgG4-RD group, seven patients had lacrimal gland involvement, five had dry eye symptoms, and six had a positive Schirmer-I test. In the SS group, 16 (94.1%) had dry eyes and all had a positive Schirmer-I test. We were able to differentiate between both diseases using levels of IL-7, IL-1α, and IL-1β; in particular, the IL-7/IL-1α and IL-7/IL-1β ratios had the best discriminatory potential, with cut-off values of 0.32 (AUC: 0.93, sensitivity: 94%, specificity: 80%, p = 0.0003) and 12.55 (AUC: 0.96, sensitivity: 94%, specificity: 90%, p = 0.0001), respectively. Our results suggest that IL-7, IL-1α, and IL-1β tear levels could help differentiate IgG4-RD from SS. Key Points • The lacrimal gland is frequently involved in IgG4-RD and SS. This characteristic makes both diseases mimics of one another. • Patients with IgG4-RD and SS have different profiles of tear cytokines and chemokines. • Tear IL-7, IL-1α, and IL-1β levels may serve as helpful biomarkers in separating IgG4-RD from SS.

Tear and Plasma Levels of Cytokines in Patients with Uveitis: Search for Active Disease Biomarkers

Uveitis accounts for up to 20% of blindness in Europe, making the development of new non-invasive biomarkers which could help in its management a field of interest. It has been hypothesised that tear levels of cytokines and chemokines could be used as a potential biomarker in patients with anterior uveitis, and this could be correlated with their concentration in plasma. Therefore, we measured twelve cytokines/chemokines in tear and plasma samples of 22 patients diagnosed with active anterior uveitis. Levels of these molecules in tears and plasma were compared and associated with the degree of activity of the uveitis. It is notable that the percentage of tear interleukin (IL)-6 detection was significantly reduced in the inactive phase (p < 0.05). However, the tear concentration in epidermal growth factor (EGF), fractalkine, IL-8, IL-1RA, interferon-inducible protein (IP)-10/CXCL10, vascular endothelial growth factor (VEGF) and IL-6, comparing the active and inactive period, was not statistically different. Apart from the tear VEGF levels, the cytokine/chemokine concentration in tears in the active/inactive phase was statistically different (p < 0.05) from the counterpart levels in plasma. In conclusion, no isolated cytokine/chemokine in the tears has been found in a concentration which could be used as a potential biomarker of disease activity and treatment response.

Mass spectrometry-based tear proteomics for noninvasive biomarker discovery

The lacrimal film has attracted increasing interest in the last decades as a potential source of biomarkers of physiopathological states, due to its accessibility, moderate complexity, and responsiveness to ocular and systemic diseases. High-performance liquid chromatography-mass spectrometry (LC-MS) has led to effective approaches to tear proteomics, despite the intrinsic limitations in sample amounts. This review focuses on the recent progress in strategy and technology, with an emphasis on the potential for personalized medicine. After an introduction on lacrimal-film composition, examples of applications to biomarker discovery are discussed, comparing approaches based on pooled-sample and single-tear analysis. Then, the most critical steps of the experimental pipeline, that is, tear collection, sample fractionation, and LC-MS implementation, are discussed with reference to proteome-coverage optimization. Advantages and challenges of the alternative procedures are highlighted. Despite the still limited number of studies, tear quantitative proteomics, including single-tear investigation, could offer unique contributions to the identification of low-invasiveness, sustained-accessibility biomarkers, and to the development of personalized approaches to therapy and diagnosis.

Sleep Loss Causes Dysfunction in Murine Extraorbital Lacrimal Glands

Purpose

Sleep loss markedly affects the structure and function of the lacrimal gland and may cause ocular surface disease as a common public health problem. This study aims to investigate the circadian disturbance caused by sleep loss leading to dysfunction of extraorbital lacrimal glands (ELGs).

Methods

A mouse sleep deprivation (SD) model for sleep loss studies was built in C57BL/6J male mice. After four weeks, the ELGs were collected at three-hour intervals during a 24-hour period. The Jonckheere-Terpstra-Kendall algorithm was used to determine the composition, phase, and rhythmicity of transcriptomic profiles in ELGs. Furthermore, we compared the non-sleep-deprived and SD-treated mouse ELG (i) reactive oxygen species (ROS) by fluorescein staining, (ii) DNA damage by immunostaining for γ-H2Ax, and (iii) circadian migration of immune cells by immunostaining for CD4, CD8, γδ-TCR, CD64, and CX3CR1. Finally, we also evaluated (i) the locomotor activity and core body temperature rhythm of mice and (ii) the mass, cell size, and tear secretion of the ELGs.

Results

SD dramatically altered the composition and phase-associated functional enrichment of the circadian transcriptome, immune cell trafficking, metabolism, cell differentiation, and neural secretory activities of mouse ELGs. Additionally, SD caused the ROS accumulation and consequent DNA damage in the ELGs, and the ELG dysfunction caused by SD was irreversible.

Conclusions

SD damages the structure, function, and diurnal oscillations of ELGs. These results highlight comprehensive characterization of insufficient sleep–affected ELG circadian transcriptome that may provide a new therapeutic approach to counteract the effects of SD on ELG function.

Fluorescence Sensing Technologies for Ophthalmic Diagnosis

Personalized and point-of-care (POC) diagnoses are critical for ocular physiology and disease diagnosis. Real-time monitoring and continuous sampling abilities of tear fluid and user-friendliness have become the key characteristics for the applied ophthalmic techniques. Fluorescence technologies, as one of the most popular methods that can fulfill the requirements of clinical ophthalmic applications for optical sensing, have been raised and applied for tear sensing and diagnostic platforms in recent decades. Wearable sensors in this case have been increasingly developed for ocular diagnosis. Contact lenses, as one of the commercialized and popular tools for ocular dysfunction, have been developed as a platform for fluorescence sensing in tears diagnostics and real-time monitoring. Numbers of biochemical analytes have been examined through developed fluorescent contact lens sensors, including pH values, electrolytes, glucose, and enzymes. These sensors have been proven for monitoring ocular conditions, enhancing and detecting medical treatments, and tracking efficiency of related ophthalmic surgeries at POC settings. This review summarizes the applied ophthalmic fluorescence sensing technologies in tears for ocular diagnosis and monitoring. In addition, the cooperation of fabricated fluorescent sensor with mobile phone readout devices for diagnosing ocular diseases with specific biomarkers continuously is also discussed. Further perspectives for the developments and applications of fluorescent ocular sensing and diagnosing technologies are also provided.

Diurnal variation on tear stability and correlation with tear cytokine concentration

PURPOSE

To investigate the effect of time of day on tear evaporation rate (TER) and tear break-up time, and its possible relationship with the concentration of inflammatory tear molecules (cytokines) in healthy subjects.

METHODS

Participants with healthy ocular surfaces attended 3 visits, including the screening visit (V0), the 2nd visit (V1) and the 3rd visit (V2). There were 7-day intervals between visits. Participants with Dry Eye Disease (DED) were excluded by using appropriate clinical tests during V0. Clinical evaluation (TER and Non-Invasive Tear Break-Up Time (NITBUT)) and tear collection were performed during V1 and V2, between 9 and 10AM and 3-4PM. The relative humidity and temperature of the examination room were also measured. The tear fluid concentrations of 15 cytokines were measured by multiplex bead analysis.

RESULTS

Seven men and 10 women (mean age ± S.D; 25.1 ± 6.63 years old) participated in the study. There were no differences in neither the TER and NITBUT outcomes, nor humidity and temperature among times or visits. Eleven out of the 15 cytokines measured were detectable in tear fluids in > 50% of the participants. In the tear levels, no significant (p > 0.05) inter- and/or intra-day differences were detected for EGF, fractalkine, IL-1RA, IL-1β and IP-10. However, significant inter-day differences were found in the tear levels of IL-10 (p = 0.027), IFN-γ (p = 0.035) and TNF-α(p = 0.04) and intra-day differences in the tear levels of IL-8/CXCL8 (p = 0.034) and MCP-1 (p = 0.002). A significant correlation between TER and IL1-β, IL-2, and Fractalkine (p = 0.03, p = 0.03 and p = 0.046, respectively) was found at V1.

CONCLUSIONS

NITBUT and TER values had no significant variability over the course of a day (AM versus PM), or on different days in healthy participants when humidity and temperature were constant. However, some tear molecule levels did show inter- and intra-day variability, having an inconsistent and moderate correlation with TER diurnal variation.

VEGF-A in Serum and Plasma Rich in Growth Factors (PRGF) Eye Drops

BACKGROUND

Vascular endothelial growth factor (VEGF)-A, the most abundant subtype of the VEGF family in the eye, plays an important role in corneal homeostasis due to its ability to mediate corneal nerve repair. Repeated intravitreal anti-VEGF injections were shown to significantly reduce corneal nerve density, which might negatively affect corneal homeostasis and lead to a neuropathic dry eye disease. Currently, there are two effective modalities to treat dry eye while supplying VEGF to the ocular surface: serum eye drops (SED) and eye drops manufactured from plasma rich in growth factors (PRGF). The purpose of this study was to measure the VEGF-A concentration in SED and PRGF eye drops.

MATERIAL AND METHODS

Ten healthy volunteers donated blood on two separate occasions, 2 - 8 days apart. Thus, a total of 20 blood samples were processed to obtain both SED and PRGF. Concentrations of VEGF-A were quantified by a Simple Plex platform run in triplicate.

RESULTS

The VEGF-A concentration in SED and PRGF was very similar between the two blood samples drawn from one individual donor but showed substantial interindividual variability. However, in all 20 samples, VEGF concentrations were substantially higher in SED samples (mean 238.7 ± 146.6 pg/mL) compared to PRGF samples (mean 67.4 ± 46.3 pg/mL). Based upon the analysis of variance (ANOVA) model for the measured concentrations with fixed effects for specimen (SED vs. PRGF) and subject, the mean difference between the SED and PRGF concentration was 168.1 pg/mL (95% confidence interval: [142.4, 193.9], p < 0.001).

CONCLUSION

Our study showed that the VEGF concentration was higher in SED than in PRGF. This is an important finding, particularly for potential treatment of dry eye disease in patients with neuropathic eye disease, especially in patients that received repeated anti-VEGF intravitreal injections, or in patients with Sjögren's disease, where the level of VEGF in tears might be pathologically decreased. Hypothetically, VEGF might be needed to restore ocular surface homeostasis. Although growing evidence has shown that VEGF-A plays an important role in corneal homeostasis, only a randomized prospective clinical trial will show whether supplying VEGF-A to the ocular surface might successfully restore the corneal homeostasis and overcome the problem of corneal neuropathy in these patients. For such a trial, based on our results, an undiluted SED should be preferred over a PRGF due to the higher content of VEGF-A.

Tear Proteomics of Children and Young Adult Soft Contact Lens, Orthokeratology and Spectacle Wearers - A Pilot Study

PURPOSE

Contact lens complications occur more often in older teenagers and young adults compared to children. This study explored differences in tear proteomics between children and young adults wearing soft contact lens (SCL), orthokeratology or spectacles for >3 years.

METHODS

Twelve children and 12 sex- and correction-matched young adults were enrolled. Tears were collected via Schirmer strips for tear proteomic analysis using mass spectrometry. Proteome Discoverer was used for protein identification. Label-Free Quantitation was generated using Scaffold software; Fisher's Exact tests were used to compare proteins by age and correction groups. Generalized linear models were used to assess differences in overall protein levels by age and correction groups. A secondary analysis of proteins presented in >50% of samples of each group was conducted using the R/Bioconductor limma package.

RESULTS

There were 385 proteins present only in young adults while 183 were unique in children. There were 528 unique proteins to SCL, 96 to orthokeratology and 149 to spectacle wearers. Based on Fisher's Exact analyses, 126 proteins were higher in young adults than children (all P < 0.048). Forty-seven protein levels were higher in SCL compared to orthokeratology (all P < 0.01), 33 protein levels were higher in SCL compared to spectacles (all P < 0.01), 15 protein levels were higher in orthokeratology compared to spectacle wearers (all P < 0.01). Based on generalized linear models, young adults had higher overall protein levels than children (P = 0.001), SCL had higher protein levels than spectacle wearers (P < 0.001) but no differences were found between orthokeratology and spectacle wearers (P = 0.79). Based on the secondary analysis, only Antileukoproteinase was higher in the young adult orthokeratology group compared to other groups (P < 0.01).

CONCLUSIONS

Tear protein type and abundance differ by age and correction. Further research is needed to understand the effects of contact lens correction in children and young adults on the tear proteome.

Mass spectrometry analysis of human tear fluid biomarkers specific for ocular and systemic diseases in the context of 3P medicine

Over the last two decades, a large number of non-communicable/chronic disorders reached an epidemic level on a global scale such as diabetes mellitus type 2, cardio-vascular disease, several types of malignancies, neurological and eye pathologies-all exerted system's enormous socio-economic burden to primary, secondary, and tertiary healthcare. The paradigm change from reactive to predictive, preventive, and personalized medicine (3PM/PPPM) has been declared as an essential transformation of the overall healthcare approach to benefit the patient and society at large. To this end, specific biomarker panels are instrumental for a cost-effective predictive approach of individualized prevention and treatments tailored to the person. The source of biomarkers is crucial for specificity and reliability of diagnostic tests and treatment targets. Furthermore, any diagnostic approach preferentially should be noninvasive to increase availability of the biomaterial, and to decrease risks of potential complications as well as concomitant costs. These requirements are clearly fulfilled by tear fluid, which represents a precious source of biomarker panels. The well-justified principle of a "sick eye in a sick body" makes comprehensive tear fluid biomarker profiling highly relevant not only for diagnostics of eye pathologies but also for prediction, prognosis, and treatment monitoring of systemic diseases. One prominent example is the Sicca syndrome linked to a cascade of severe complications that include dry eye, neurologic, and oncologic diseases. In this review, protein profiles in tear fluid are highlighted and corresponding biomarkers are exemplified for several relevant pathologies, including dry eye disease, diabetic retinopathy, cancers, and neurological disorders. Corresponding analytical approaches such as sample pre-processing, differential proteomics, electrophoretic techniques, high-performance liquid chromatography (HPLC), enzyme-linked immuno-sorbent assay (ELISA), microarrays, and mass spectrometry (MS) methodology are detailed. Consequently, we proposed the overall strategies based on the tear fluid biomarkers application for 3P medicine practice. In the context of 3P medicine, tear fluid analytical pathways are considered to predict disease development, to target preventive measures, and to create treatment algorithms tailored to individual patient profiles.

Age and sex-specific differences in interleukin 4, interferon gamma, macrophage migration inhibitory factor, and vascular endothelial growth factor levels in the tears of healthy subjects

OBJECTIVE

To investigate the physiological profile of pro-inflammatory and anti-inflammatory cytokines in tears produced by epithelial cells under the effect of endogenous and exogenous biological factors. Knowing the physiological cytokine profile in tears with its biological characteristics including sex- and age-specific effects is fundamental when tears are analyzed for diagnostic or prognostic purposes in eye diseases.

METHODS

Tear samples were collected from right eye of 45 healthy volunteers (24 males, 21 females) by 5 μl microcapillary tube. Cytokines interleukin 1β, interleukin 10, interleukin 4, interferon gamma, macrophage migration inhibitory factor, and vascular endothelial growth factor were quantified by multiplex Bio-Plex system.

RESULTS

The production of macrophage migration inhibitory factor cytokine by epithelial cells on the ocular surface is higher in males compared to females (p = 0.05); actually, most of female tear samples present with undetectable macrophage migration inhibitory factor levels. Our results show the negative correlations between the age and concentrations of interleukin 4 (p < 0.01) and interferon gamma (p < 0.01) in tears, respectively, and positive associations of vascular endothelial growth factor levels with the age above 45 years (p < 0.05).

CONCLUSIONS

Data in this study indicate that age and sex may affect the physiological levels of cytokines in tears. Consequently, the impacts of biological factors need to be recognized and taken into consideration before the levels of cytokines in patients' tears are analyzed for medical reasons. Concentrations of interleukin 1β and interleukin 10 cytokines, however, are very low in healthy tears and do not seem to be influenced by studied biological factors; therefore, they meet the requirements for analytes suitable for medical diagnostic and prognostic purposes.

Ophthalmic sensing technologies for ocular disease diagnostics

Point-of-care diagnosis and personalized treatments are critical in ocular physiology and disease. Continuous sampling of tear fluid for ocular diagnosis is a need for further exploration. Several techniques have been developed for possible ophthalmological applications, from traditional spectroscopies to wearable sensors. Contact lenses are commonly used devices for vision correction, as well as for other therapeutic and cosmetic purposes. They are increasingly being developed into ocular sensors, being used to sense and monitor biochemical analytes in tear fluid, ocular surface temperature, intraocular pressure, and pH value. These sensors have had success in detecting ocular conditions, optimizing pharmaceutical treatments, and tracking treatment efficacy in point-of-care settings. However, there is a paucity of new and effective instrumentation reported in ophthalmology. Hence, this review will summarize the applied ophthalmic technologies for ocular diagnostics and tear monitoring, including both conventional and biosensing technologies. Besides applications of smart readout devices for continuous monitoring, targeted biomarkers are also discussed for the convenience of diagnosis of various ocular diseases. A further discussion is also provided for future aspects and market requirements related to the commercialization of novel types of contact lens sensors.

Signature of Circulating Biomarkers in Recurrent Non-Infectious Anterior Uveitis. Immunomodulatory Effects of DHA-Triglyceride. A Pilot Study

The purpose of this study was to identify circulating biomarkers of recurrent non-infectious anterior uveitis (NIAU), and to address the anti-inflammatory effects of triglyceride containing docosahexaenoic acid (DHA-TG). A prospective multicenter study was conducted in 72 participants distributed into: patients diagnosed with recurrent NIAU in the quiescence stage (uveitis group (UG); n = 36) and healthy controls (control group (CG); n = 36). Each group was randomly assigned to the oral supplementation of one pill/day (+) containing DHA-TG (n = 18) or no-pill condition (-) (n = 17) for three consecutive months. Data from demographics, risk factors, comorbidities, eye complications and therapy were recorded. Blood was collected and processed to determine pro-inflammatory biomarkers by bead-base multiplex assay. Statistical processing with multivariate statistical analysis was performed. The mean age was 50, 12 (10, 31) years. The distribution by gender was 45% males and 55% females. The mean number of uveitis episodes was 5 (2). Higher plasma expression of interleukin (IL)-6 was detected in the UG versus the CG (p = 5 × 10-5). Likewise, significantly higher plasma levels were seen for IL-1β, IL-2, INFγ (p = 10-4), and TNFα (p = 2 × 10-4) in the UG versus the CG. Significantly lower values of the above molecules were found in the +DHA-TG than in the -DHA-TG subgroups, after 3 months of follow-up, TNFα (p = 10-7) and IL-6 (p = 3 × 10-6) being those that most significantly changed. Signatures of circulating inflammatory mediators were obtained in the quiescent stage of recurrent NIAU patients. This 3-month follow-up strongly reinforces that a regular oral administration of DHA-TG reduces the inflammatory load and may potentially supply a prophylaxis-adjunctive mediator for patients at risk of uveitis vision loss.

Protein Microarrays for Ocular Diseases

The eye is a multifaceted organ organized in several compartments with particular properties that reflect their diverse functions. The prevalence of ocular diseases is increasing, mainly because of its relationship with aging and of generalized lifestyle changes. However, the pathogenic molecular mechanisms of many common eye pathologies remain poorly understood. Considering the unquestionable importance of proteins in cellular processes and disease progression, proteomic techniques, such as protein microarrays, represent a valuable approach to analyze pathophysiological protein changes in the ocular environment. This technology enables to perform multiplex high-throughput protein expression profiling with minimal sample volume requirements broadening our knowledge of ocular proteome network in eye diseases.In this review, we present a brief summary of the main types of protein microarrays (antibody microarrays, reverse-phase protein microarrays, and protein microarrays) and their application for protein change detection in chronic ocular diseases such as dry eye, age-related macular degeneration, diabetic retinopathy, and glaucoma. The validation of these specific protein changes in eye pathologies may lead to the identification of new biomarkers, depiction of ocular disease pathways, and assistance in the diagnosis, prognosis, and development of new therapeutic options for eye pathologies.

Correlations between tear fluid and aqueous humor cytokine levels in bullous keratopathy

PURPOSE

To evaluate the correlation between tear fluid and aqueous humor (AqH) cytokine levels in eyes with bullous keratopathy (BK) and with normal endothelium.

METHODS

This prospective consecutive case-series study included 71 eyes of 71 patients: 31 eyes with BK, 18 eyes with non-BK corneal diseases, and 22 eyes with uncomplicated cataract (healthy controls). Total protein and cytokine (interleukin [IL]-1α, IL-1β, IL-4, IL-6, IL-8, IL-10, MIP-1α, MIP-1β, monocyte chemotactic protein [MCP]-1, E-selectin, P-selectin, soluble intercellular adhesion molecule [sICAM]-1, and IP-10) levels in the tear fluid and AqH were measured using multiplex beads immunoassay. The correlations between tear and AqH cytokine levels were assessed.

RESULTS

The AqH protein level was significantly higher in BK eyes (1.09 ± 0.08 mg/mL) than in non-BK (0.63 ± 0.11, P = 0.0004) and healthy control (0.62 ± 0.06, P = 0.0002) eyes. The tear total protein and IL-4 levels were significantly higher in the BK group compared to healthy controls (P = 0.0374 and 0.0032, respectively). The AqH IL-8 and sICAM-1 levels were significantly higher in the BK group compared to controls (P = 0.0001 and 0.0083, respectively). In BK eyes, the tear IL-4 level was significantly correlated with the MCP-1(r = 0.563, P = 0.001) and total protein (r = 0.589, P = 0.001) AqH levels. The tear IL-8 level was significantly correlated with the MCP-1(r = 0.598, p = 0.001) and IL-4 (r = 0.781, p < 0.0001) AqH levels in BK eyes. However, no significant correlations were found between tear and AqH cytokine levels in non-BK and healthy controls eyes.

CONCLUSIONS

The tear cytokine levels are correlated with those of AqH only in BK, but not in non-BK and healthy controls.

Dry Eye Disease and Tear Cytokine Levels-A Meta-Analysis

Background—It is recognized that inflammation is an underlying cause of dry eye disease (DED), with cytokine release involved. We systematically reviewed literature with meta-analyses to quantitatively summarize the levels of tear cytokines in DED. Methods—The PubMed, Embase, Web of Science, Ovid, Cochrane, and Scopus databases were reviewed until September 2019, and original articles investigating tear cytokines in DED patients were included. Differences of cytokines levels of DED patients and controls were summarized by standardized mean differences (SMD) using a random effects model. Study quality was assessed by applying Newcastle-Ottawa-Scale and the GRADE quality score. Methods of analytical procedures were included as covariate. Results—Thirteen articles investigating 342 DED patients and 205 healthy controls were included in the meta-analysis. The overall methodological quality of these studies was moderate. Systematic review of the selected articles revealed that DED patients had higher tear levels of interleukin (IL)-1β, IL-6, chemokine IL-8, IL-10, interferon-γ, IFN-γ, and tumor necrosis factor-α, TNF-α as compared to controls. Evidence was less strong for IL-2 and IL-17A. Conclusions—Data show that levels of tear cytokines in DED and control display a great variability, and further studies of higher quality enrolling a higher number of subjects are needed, to define a cut-off value.

Tear Inflammatory Molecules in Contact Lens Wearers: A Literature Review

Background:

Numerous studies have analysed the effect of using different Contact Lenses (CLs) or care solutions, and suffering discomfort or diseases associated with CL wear on the inflammatory mediator release into the tears.

Objective:

To summarize the published data on tear inflammatory molecules related to CL use.

Methods:

A PubMed-NCBI search has been conducted and those publications which carried out original investigations including the analysis of tear inflammatory mediators in CL wearers were selected.

Results:

Forty-three articles, from 1990 to 2019, have been included. Wearing hydrogel CLs, rigid gas permeable CLs, and special designs for irregular corneas in keratoconus patients (CLs with keratoconic design, hybrid CLs, piggyback fit, and scleral CLs) have been reported to alter the concentration of several molecules in tears. Moreover, there seems to be an effect of the wearing time and schedule, CL materials and designs, and care solutions used. Regarding CL discomfort, its relation with inflammatory mediators is not clear. However, some diseases associated to CL wear, such as giant papillary conjunctivitis, CL induced acute red eye, CL induced peripheral ulcer, and acanthamoeba keratitis have been related to the release of certain inflammatory mediators, which may serve as potential biomarkers.

Conclusion:

There is evidence suggesting that different aspects of CL wear alter the inflammatory mediator profile in tears, which may indicate an inflammatory state of the lacrimal functional unit. However, more studies need to be carried out to better understand how this inflammatory process works and its repercussion on the different aspects of CL wear.

Substance P Level in Tears as a Potential Biomarker for Contact Lens Discomfort

Purpose: To analyze the effects of contact lens (CL) wear, time of the day, and CL discomfort (CLD) on clinical signs, tear inflammatory mediators and substance P.Methods: Thirty symptomatic and 30 asymptomatic CL wearers attended two visits (morning and afternoon) on two days (non-CL and CL wearing days). Comfort, meniscus area, noninvasive breakup time (NIBUT), tear collection, hyperemia, lid parallel conjunctival folds, fluorescein staining, and sensitivity were performed. The tear levels of 23 inflammatory mediators and substance P were measured.Results: Comfort, meniscus area, NIBUT, and MMP-9 were lower while conjunctival staining and EGF higher (p ≤ 0.015) on the CL wearing day. Comfort, IL-8/CXCL8, and VEGF were lower while EGF, IP-10/CXCL10, and MCP-1/CCL2 higher (p ≤ 0.047) in the afternoon. Comfort was lower and substance P higher (p ≤ 0.006) in symptomatic wearers.Conclusion: Substance P may be implicated in CLD etiology; its role and potential application as a biomarker should be further studied.

What information can be obtained from the tears of a patient with primary open angle glaucoma?

Since tears are a biological fluid, they have a potential diagnostic value for ophthalmic diseases. The aim of this study was to compare tear supernatants and pellets obtained from patients suffering from primary open angle glaucoma (POAG) and healthy persons (HPs) using transmission electron microscopy (TEM) and molecular biological methods. Tear supernatants and pellets were prepared using ultrafiltration and ultracentrifugation and were examined by negative staining and immunogold labelling TEM. DNA of the pellets was isolated, quantified and sequenced using a MiSeq (Illumina, USA) genomic sequencer with the Reagent Kit v3 (600 cycles, Illumina, USA). MicroRNA was isolated and quantified from the pellets; miR-146b, miR-16 and miR-126 were detected using TaqMan MicroRNA Assays (Applied Biosystems, USA). TEM of tear supernatants from both POAG patients and HPs revealed identical constituents: spherical or cup-shaped vesicles, "non-vesicles", cell debris and macromolecular aggregates. Pellets of POAG patients and HPs contained small extracellular vesicles (sEVs) non-labelled vesicles and "non-vesicles"; pellets of sick persons also contained sEVs with "a capsule". POAG-patient tear pellets showed elevated concentrations of genomic ds-DNA and SINE-repeats, and different expressions of miR-146b, miR-16 and miR-126 and a different set of bacterial DNA in comparison with pellets obtained from the tears of HPs. The data obtained indicate that the tears of HPs and POAG patients could serve as an object for TEM studies and as a source of sEV-containing preparations (pellets), which, in turn, could be used for the isolation and study of genomic ds-DNA and RNA. Our data provide the basis for using tears for diagnostic applications.

Review of Biomarkers in Ocular Matrices: Challenges and Opportunities

Biomarkers provide a powerful and dynamic approach to improve our understanding of the mechanisms underlying ocular diseases with applications in diagnosis, disease modulation or for predicting and monitoring of clinical response to treatment. Defined as measurable indicator of normal or pathological processes, biomarker evaluation has been used extensively in drug development within clinical settings to better comprehend effectiveness of treatment in ocular diseases. Biomarkers in the eye have the advantage of access to multiple ocular matrices via minimally invasive methods. Repeat sampling for biomarker assessment has enabled reproducible objective measures of disease process or biological responses to a drug treatment. This review describes the usage of biomarkers with respect to four commonly sampled ocular matrices in clinic: tears, conjunctiva, aqueous humor and vitreous. Issues that affect the evaluation of biomarkers are discussed along with opportunities to leverage biomarkers such that ultimately, they can be used for customized targeted therapy.

Detection of Lipid Mediators of Inflammation in the Human Tear Film

PURPOSE

Lipid mediators of inflammation are a group of signaling molecules produced by various cells under physiological conditions and modulate the inflammatory process during various pathologic conditions. Although eicosanoids and F2-isoprostanes are recognized lipid mediators of inflammation, there is no consensus yet on the extraction and mass spectrometry (MS) method for their analysis in individual human tear samples. Thus, the aim of this study was to develop an optimal method for extraction of lipid mediators of inflammation in the tear film and evaluate MS techniques for their analysis.

METHODS

Basal tears were collected from each eye of 19 subjects using glass microcapillaries. Lipid extraction was performed using either varying concentrations of acidified methanol, a modified Folch method, or solid-phase extraction. Initially, an untargeted analysis of the extracts was performed using SCIEX TripleTOF 5600 mass spectrometer to identify any lipid mediators of inflammation (eicosanoids) and later a targeted analysis was performed using the SCIEX 6500 Qtrap to identify and quantify prostaglandins and isoprostanes. Mass spectra and chromatograms were analyzed using Peakview, XCMS, and Multiquant software.

RESULTS

Prostaglandins and isoprostanes were observed and quantified using the Qtrap mass spectrometer under multiple reaction monitoring (MRM) mode after solid-phase extraction. Extraction with acidified methanol along with the Folch method produced cleaner spectra during MS with the Triple time of flight (TOF) mass spectrometer. Lipid mediators of inflammation were not observed in any of the tear samples using the Triple TOF mass spectrometer.

CONCLUSIONS

Solid-phase extraction may be the method of choice for extraction of prostaglandins and isoprostanes in low volumes of tears. The SCIEX Qtrap 6500 in MRM mode may be suitable to identify and quantify similar lipid mediators of inflammation.

Level of tear cytokines in population-level participants and correlation with clinical features

AIMS

Tear cytokine levels indicate severity of ocular surface inflammation. Previous reports of cytokine concentrations were based on hospital-based studies or non-Chinese populations. We determine the range of tear concentration of cytokines in a representative adult Chinese population.

METHODS

Thirty-nine participants were recruited from a population-based study of Chinese adults in Singapore, and standardized clinical ocular surface/eyelid features evaluated. Tear was extracted from Schirmer strips and analysed using a multiplex bead-based assay.

RESULTS

Tear concentrations of 14 cytokines were investigated and quantifiable in each participant. Eight cytokines increased with increasing age, and 4 cytokines (IL-4, IL-12, IL-10 and IFN-γ) were increased in people with increased frequency of ocular discomfort. Three cytokines (MCP-1, IP-10 and IL-13) had increased levels in people with lower Schirmer tests, while 9 other cytokines were increased in patients with eyelid crusting (TNF-α, IL-1β, IL-17α, IL-2, IL-4, IL-6, IL-12, IL-10 and IFN-γ). Twelve percent of participants had eyelid crusting.

CONCLUSION

Using a convenient collection technique that is a routine clinical test, 14 tear cytokines could be quantifiable even in Singapore Chinese adults without a dry eye diagnosis. Elevation of different tear cytokines may be linked to subclinical aqueous tear deficiency or eyelid inflammation even in asymptomatic people.

Corneal Sensitivity and Inflammatory Biomarkers in Contact Lens Discomfort

PURPOSE

The aim of this study was to analyze whether symptoms of discomfort in hydrogel contact lens (HCL) wearers were associated with changes in corneal sensitivity or levels of tear inflammatory mediators.

METHODS

Sixty-six subjects were included: 47 HCL wearers, further divided into 24 symptomatic and 23 asymptomatic wearers by the Contact Lens Dry Eye Questionnaire short form and 19 non-contact lens wearers. At least 24 h after HCL removal, we obtained scores from the Ocular Surface Disease Index and mechanical, hot, and cold corneal thresholds using a Belmonte esthesiometer. We collected 4 μl of tears with a capillary micropipette and measured levels of 12 inflammatory markers using a bead-based array: epidermal growth factor, fractalkine, interleukin-10 (IL-10), IL-1β, IL-1 receptor antagonist, IL-2, IL-4, IL-6, IL-8, monocyte chemoattractant protein 1, tumor necrosis factor-α, and matrix metalloproteinase 9.

RESULTS

There were no significant differences between groups in corneal sensitivity thresholds and levels of tear molecules. The following significant correlations were found in the total sample pooled: Ocular Surface Disease Index correlated with mechanical threshold (p < 0.01; rho = -0.324) and epidermal growth factor (p < 0.01, rho = -0.330), and mechanical threshold correlated with heat threshold (p < 0.01, rho = -0.321).

CONCLUSIONS

Twenty-four hours after HCL removal, symptoms of discomfort in HCL wearers are not related to changes in corneal sensitivity or tear inflammatory mediator levels. This might indicate either that HCL wear has no effect on these parameters or that ocular surfaces recover from HCL-caused effects during the first hours after HCL removal. However, there were correlations for associations between symptoms, corneal sensitivity, and some molecules in tears.

Evaluation of commonly used tear sampling methods and their relevance in subsequent biochemical analysis

The human precorneal tear film is a special body fluid, since it is a complex mixture of proteins, lipids, small bioactive molecules, and their concentrations and relative distribution represent not only the metabolic state of the ocular surface but also the systemic and local homeostasis of the outer eye and the human body. This suggests that biochemical analysis of the precorneal tear film composition may provide a non-invasive tool for diagnosis and monitoring of disease progression or treatment efficacy in human medicine. However, collecting tears is demanding, and obtaining reproducible and unaltered samples is challenging because of the small sample volumes of tears. Several methods are available for tear collection as a preparatory step of precorneal tear film analysis, and the collection method used has to be assessed since it has a critical impact on the effectiveness of the assays and on the quality of the results. Each sampling method has advantages and disadvantages; therefore, it is not easy to choose the appropriate collecting method for tear collection. To overcome these limitations various methods have been recommended by different authors for special aspects of specific tests. The aim of our review was to evaluate tear sampling methods with regard to our ongoing biochemical analysis.

Tear Cytokine Levels in Contact Lens Wearers With Acanthamoeba Keratitis

PURPOSE

To determine differences in key tear film cytokines between mild and severe cases of acanthamoeba keratitis (AK) and control contact lens (CL) wearers.

METHODS

This was a prospective study of CL wearers with AK attending Moorfields Eye Hospital and control CL wearers from the Institute of Optometry, London. Basal tear specimens were collected by 10-μL capillary tubes (BLAUBRAND intraMark, Wertheim, Germany), and tear protein levels were measured with a multiplex magnetic bead array (Luminex 100; Luminex Corporation, Austin, TX) for cytokines interleukin (IL)-1β, IL-6, IL-8, IL-10, IL-17A, IL-17E, IL-17F, IL-22, and interferon gamma and with enzyme-linked immunosorbent assay (Abcam, Cambridge, United Kingdom) for CXCL2. Severe cases of AK were defined as having active infection for over 12 months and at least 1 severe inflammatory event.

RESULTS

One hundred and thirty-two tear samples were collected from a total of 61 cases (15 severe and 46 mild-moderate) and 22 controls. IL-8, part of the Toll-like receptor 4 cytokine cascade, was found to be expressed at a detectable level more often in cases of AK than in control CL wearers (P = 0.003) and in higher concentrations in severe cases than in milder forms of the disease (z = -2.35). IL-22, part of the IL-10 family, and a proinflammatory Th17 cytokine, was detected more often in severe cases than in milder forms of AK (P < 0.02).

CONCLUSIONS

Profiling patients with AK during disease shows differences in cytokine levels between severe and milder disease that may inform clinical management. The Toll-like receptor 4 and IL-10/Th17 inflammatory pathways should be included in further investigations of this disease.

Changes in Tear Cytokine Concentrations Following Discontinuation of Soft Contact Lenses-A Pilot Study

PURPOSE

This study investigated changes in selected tear cytokine concentrations (IL-1β, IL-1Ra, IL-6, IL-10, IL-12 (p70), and TNF-α) after a 1-week washout from soft contact lens wear (CLW), and the repeatability of cytokine measurements using custom multiplex assays.

METHODS

A total of 10 subjects completed this 6-visit (immediately following contact lens removal, and after 1, 2, 3, 4, and 7 [±1] days without CLW) pilot study. Approximately 20 to 30 μL of pooled basal tears were collected from both eyes at each visit. Two custom multiplex assays were used by two operators to quantify the concentration of tear cytokines. Tear samples from subjects 1 to 6 were analyzed using the first kit by operator 1. Tear samples from subject 7 to 10 plus additional tear samples from subjects 1 to 5, which were used to determine the between-kit per operator repeatability, were analyzed using the second kit by operator 2. Linear mixed models were used to determine changes in tear cytokine concentrations over time. Between-kit per operator and within-kit per operator repeatabilities were assessed using the Bland and Altman analysis.

RESULTS

There were no significant changes in tear cytokine concentrations over a 1-week washout of CLW. More than 99% of the tear samples had detectable levels of cytokines using custom multiplex assays. Within-kit per operator repeatability was good, but between-kit per operator repeatability was poor; likely due to protein degradation, differences in operator experience, and operating procedures.

CONCLUSION

A washout period may not be necessary when evaluating changes in tear cytokines with new contact lenses or lens care products. A well-trained operator using standardized operating procedures can produce repeatable measurements using custom multiplex assays.