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Gijs M, Arumugam S, van de Sande N, Webers CAB, Sethu S, Ghosh A, Shetty R, Vehof J, Nuijts RMMA. Pre-analytical sample handling effects on tear fluid protein levels. Sci Rep 2023; 13:1317. [PMID: 36693949 PMCID: PMC9873914 DOI: 10.1038/s41598-023-28363-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2022] [Accepted: 01/16/2023] [Indexed: 01/25/2023] Open
Abstract
Tear fluid is emerging as a source of non-invasive biomarkers, both for ocular and systemic conditions. Accurate quantification of tear proteins can be improved by standardizing methods to collect and process tear fluid. The aim of this study was to determine sample handling factors that may influence the tear protein biomarker profile. Tear fluid was collected using Schirmer's strips. Tear proteins were extracted by elution through centrifugation. Total protein content was determined using the bicinchoninic acid assay. Key concepts that apply to the entire sample processing cycle are tear sampling, tear storage, protein extraction and data normalization. Differences in wetting or migration length were observed between Schirmer's strips from different manufacturers, and between protein-free and protein-rich solutions. One unit of migration length (mm) did not correspond to one unit of volume (µL). A positive correlation (r = 0.6671, p < 0.0001) was observed between migration length and total tear protein content. The most beneficial storage conditions were strips that were not stored (+ 21.8%), or underwent 'wet' storage (+ 11.1%). Protein recovery was the highest in 400 µL extraction buffer and independent of protein molecular weight. This study helps to explain inter- and intra-variability that is often seen with tear biomarker research. This information is critical to ensure accuracy of test results, as tear biomarkers will be used for patient management and in clinical trials in the near future. This study also highlights the need for standardization of Schirmer's strip manufacturing, tear fluid processing and analyte concentration normalization.
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Affiliation(s)
- Marlies Gijs
- University Eye Clinic Maastricht, School for Mental Health and Neuroscience (MHeNs), Maastricht University Medical Center (MUMC+), P. Debyelaan 25, 6229 HX, Maastricht, The Netherlands.
| | - Sinthuja Arumugam
- University Eye Clinic Maastricht, School for Mental Health and Neuroscience (MHeNs), Maastricht University Medical Center (MUMC+), P. Debyelaan 25, 6229 HX, Maastricht, The Netherlands
| | - Nienke van de Sande
- University Eye Clinic Maastricht, School for Mental Health and Neuroscience (MHeNs), Maastricht University Medical Center (MUMC+), P. Debyelaan 25, 6229 HX, Maastricht, The Netherlands
| | - Carroll A B Webers
- University Eye Clinic Maastricht, School for Mental Health and Neuroscience (MHeNs), Maastricht University Medical Center (MUMC+), P. Debyelaan 25, 6229 HX, Maastricht, The Netherlands
| | - Swaminathan Sethu
- GROW Research Laboratory, Narayana Nethralaya Foundation, Bangalore, India
| | - Arkasubhra Ghosh
- GROW Research Laboratory, Narayana Nethralaya Foundation, Bangalore, India
| | - Rohit Shetty
- University Eye Clinic Maastricht, School for Mental Health and Neuroscience (MHeNs), Maastricht University Medical Center (MUMC+), P. Debyelaan 25, 6229 HX, Maastricht, The Netherlands.,GROW Research Laboratory, Narayana Nethralaya Foundation, Bangalore, India.,Department of Cornea and Refractive Surgery, Narayana Nethralaya, Bangalore, India
| | - Jelle Vehof
- Department of Ophthalmology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.,Dutch Dry Eye Clinic, Velp, The Netherlands.,Department of Ophthalmology, Vestfold Hospital Trust, Tønsberg, Norway
| | - Rudy M M A Nuijts
- University Eye Clinic Maastricht, School for Mental Health and Neuroscience (MHeNs), Maastricht University Medical Center (MUMC+), P. Debyelaan 25, 6229 HX, Maastricht, The Netherlands.,Department of Ophthalmology, Zuyderland Medical Center, Heerlen, The Netherlands
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Gijs M, Veugen JMJ, Wolffs PFG, Savelkoul PHM, Tas J, van Bussel BCT, de Kruif MD, Henry RMA, Webers CAB, Dickman MM, Nuijts RMMA. In-Depth Investigation of Conjunctival Swabs and Tear Fluid of Symptomatic COVID-19 Patients, an Observational Cohort Study. Transl Vis Sci Technol 2021; 10:32. [PMID: 34673905 PMCID: PMC8543390 DOI: 10.1167/tvst.10.12.32] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2021] [Accepted: 09/15/2021] [Indexed: 01/08/2023] Open
Abstract
Purpose The putative presence of SARS-CoV-2 in ocular specimen puts healthcare workers at risk. We thoroughly examined conjunctival swabs and tear fluid in a large cohort of COVID-19 patients. Methods A total of 243 symptomatic laboratory-confirmed COVID-19 patients were included in this observational multicenter study. Conjunctival swabs were analyzed by reverse transcription polymerase chain reaction for detection of SARS-CoV-2 RNA. Next-generation sequencing and phylogenetic analysis were performed to identify viral strains and to determine tissue tropism. Schirmer tear samples from 43 hospitalized COVID-19 patients and 25 healthy controls were analyzed by multiplex cytokine immunoassays. Results Viral SARS-CoV-2 RNA was detected in conjunctival swabs from 17 (7.0%) of 243 COVID-19 patients. Conjunctival samples were positive for viral SARS-CoV-2 RNA as long as 12 days after disease onset. Cycle threshold (Ct) values for conjunctival swabs (mean 34.5 ± 5.1) were significantly higher than nasopharyngeal swabs (mean 16.7 ± 3.6). No correlation between Ct values of conjunctival and nasopharyngeal swabs was observed. The majority of positive conjunctival samples were detected only once and primarily during the first visit. Next-generation sequencing analysis revealed that the virus strain found in the conjunctiva was most often identical to the one found in the nasopharynx. Tear cytokine levels IL-1β and IL-6 were elevated in COVID-19 patients compared to healthy controls. Conclusions Conjunctival samples that were positive for SARS-CoV-2 RNA contained the same viral strain as the nasopharynx. Translational Relevance The presence of SARS-CoV-2 viral RNA and elevated cytokines in tear fluid confirm the involvement of the ocular surface in COVID-19 disease.
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Affiliation(s)
- Marlies Gijs
- University Eye Clinic Maastricht, Maastricht University Medical Center, Maastricht, the Netherlands
- School for Mental Health and Neuroscience (MHeNs), Maastricht University, Maastricht, the Netherlands
| | - Judith M. J. Veugen
- University Eye Clinic Maastricht, Maastricht University Medical Center, Maastricht, the Netherlands
- School for Mental Health and Neuroscience (MHeNs), Maastricht University, Maastricht, the Netherlands
- Department of Medical Microbiology, Maastricht University Medical Center, Maastricht, the Netherlands
- Care and Public Health Research Institute (CAPHRI), Maastricht University, Maastricht, the Netherlands
| | - Petra F. G. Wolffs
- Department of Medical Microbiology, Maastricht University Medical Center, Maastricht, the Netherlands
- Care and Public Health Research Institute (CAPHRI), Maastricht University, Maastricht, the Netherlands
| | - Paul H. M. Savelkoul
- Department of Medical Microbiology, Maastricht University Medical Center, Maastricht, the Netherlands
- Department of Medical Microbiology and Infection Control, Amsterdam Infection and Immunity Institute, Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands
| | - Jeanette Tas
- School for Mental Health and Neuroscience (MHeNs), Maastricht University, Maastricht, the Netherlands
- Department of Intensive Care Medicine, Maastricht University Medical Center, Maastricht, the Netherlands
| | - Bas C. T. van Bussel
- Care and Public Health Research Institute (CAPHRI), Maastricht University, Maastricht, the Netherlands
- Department of Intensive Care Medicine, Maastricht University Medical Center, Maastricht, the Netherlands
| | - Martijn D. de Kruif
- Department of Pulmonary Medicine, Zuyderland Medical Center, Heerlen, the Netherlands
| | - Ronald M. A. Henry
- Department of Internal Medicine, Maastricht University Medical Center, Maastricht, the Netherlands
| | - Carroll A. B. Webers
- University Eye Clinic Maastricht, Maastricht University Medical Center, Maastricht, the Netherlands
- School for Mental Health and Neuroscience (MHeNs), Maastricht University, Maastricht, the Netherlands
| | - Mor M. Dickman
- University Eye Clinic Maastricht, Maastricht University Medical Center, Maastricht, the Netherlands
- School for Mental Health and Neuroscience (MHeNs), Maastricht University, Maastricht, the Netherlands
| | - Rudy M. M. A. Nuijts
- University Eye Clinic Maastricht, Maastricht University Medical Center, Maastricht, the Netherlands
- School for Mental Health and Neuroscience (MHeNs), Maastricht University, Maastricht, the Netherlands
- Department of Ophthalmology, Zuyderland Medical Center, Heerlen, the Netherlands
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