Diurnal variation on tear stability and correlation with tear cytokine concentration

Temporal variations in meibomian gland structure-A pilot study

PURPOSE

To investigate whether there is a measurable change in meibomian gland morphological characteristics over the course of a day (12 h) and over a month.

METHODS

The study enrolled 15 participants who attended a total of 11 study visits spanning a 5-week period. To assess diurnal changes in meibomian glands, seven visits were conducted on a single day, each 2 h apart. For monthly assessment, participants attended an additional visit at the same time of the day every week for three consecutive weeks. Meibography using the LipiView® II system was performed at each visit, and meibomian gland morphological parameters were calculated using custom semi-automated software. Specifically, six central glands were analysed for gland length ratio, gland width, gland area, gland intensity and gland tortuosity.

RESULTS

The average meibomian gland morphological metrics did not exhibit significant changes during the course of a day or over a month. Nonetheless, certain individual gland metrics demonstrated notable variation over time, both diurnally and monthly. Specifically, meibomian gland length ratio, area, width and tortuosity exhibited significant changes both diurnally and monthly when assessed on a gland-by-gland basis.

CONCLUSIONS

Meibomian glands demonstrated measurable structural change over short periods of time (hours and days). These results have implications for innovation in gland imaging and for developing precision monitoring of gland structure to assess meibomian gland health more accurately.

Tear Cytokines as Predictive Biomarkers of Success in Contact Lens Discomfort Management

PURPOSE

To analyze changes in tear levels of inflammatory mediators in symptomatic contact lens (CL) wearers after refitting with daily disposable CLs and to identify potential biomarkers of success in CL discomfort (CLD) management.

METHODS

Symptomatic CL wearers (CLDEQ-8 ≥ 12) were refitted (V1) with daily disposable CLs (Delefilcon A). After one month (V2), participants were classified into the post-fitting non-symptomatic (CLDEQ <12) and symptomatic (CLDEQ ≥12) groups. At each visit, the participants were clinically evaluated, tears were collected, and 20 inflammatory mediators and substance P (SP) were measured using multiplex immunobead analysis and ELISA, respectively. The detection rates and concentrations were compared between visits and groups, and logistic regression models were performed.

RESULTS

Forty-three subjects (32 women/11 men; mean age: 23.2 ± 4.9 years) were enrolled. The IL-1β and IL-9 detection rates were higher at V2 (p ≤ 0.044). The detection rates of IL-1β, IL-9, MIP-1α/CCL3, and MMP-9 at V1 (p ≤ 0.045) and IL-17A at V2 (p ≤ 0.014) were higher in the post-fitting symptomatic group. The tear IL-9 concentration was increased at V2 (p = 0.018). The tear concentrations of fractalkine/CX3CL1, IL-2, IL-6, IL-10, MCP-3/CCL7, MIP-1β, NGF, RANTES/CCL5, and TNF-α were higher in the post-fitting symptomatic group (p ≤ 0.044). Additionally, levels of fractalkine/CX3CL1, IL-2, IL-6, IL-10, RANTES/CCL5, and TNF-α at V1 were significantly associated with the post-fitting grouping (p ≤ 0.044).

CONCLUSIONS

Low tear concentrations of specific inflammatory mediators may be used as a predictive biomarker of success for refitting symptomatic CL wearers with daily disposable CLs. However, complementary treatments might be required for symptomatic CL wearers with higher levels of these inflammatory molecules.

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.

Unrevealing the connection between real sample analysis and analytical method. The case of cytokines

Cytokines are compounds that belong to a special class of signaling biomolecules that are responsible for several functions in the human body, being involved in cell growth, inflammatory, and neoplastic processes. Thus, they represent valuable biomarkers for diagnosing and drug therapy monitoring certain medical conditions. Because cytokines are secreted in the human body, they can be detected in both conventional samples, such as blood or urine, but also in samples less used in medical practice such as sweat or saliva. As the importance of cytokines was identified, various analytical methods for their determination in biological fluids were reported. The gold standard in cytokine detection is considered the enzyme-linked immunosorbent assay method and the most recent ones have been considered and compared in this study. It is known that the conventional methods are accompanied by a few disadvantages that new methods of analysis, especially electrochemical sensors, are trying to overcome. Electrochemical sensors proved to be suited for the elaboration of integrated, portable, and wearable sensing devices, which could also facilitate cytokines determination in medical practice.

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.

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.

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.