This experimental study of the tear fluid proteome demonstrated that the proteins found in the tear fluid of multiple sclerosis patients are modified and may indicate inflammation, which can be helpful in the diagnosis and treatment of these patients.
Multiple sclerosis (MS) is a neurodegenerative condition that involves the central nervous system (CNS). The diagnostic modalities include clinical evaluation, neuroimaging, and examination of the cerebrospinal fluid; however, there is no specific diagnostic measure for MS. While tear fluid is not commonly used in laboratories, it can serve as an effective tool in formulating a non-invasive diagnosis of MS.
This pilot proteomic analysis utilized different experimental methods to identify the tear fluid composition of MS patients and concluded that the tear proteome is altered in MS patients, which may indicate inflammation and support the diagnosis of MS. The study findings are published in the journal Sensors (Basel, Switzerland).
Patient and Study Characteristics
This pilot experimental analysis obtained basal tear fluid present in the lower eyelid from 10 healthy subjects and 20 MS patients using glass micro capillaries. The analysis was performed using atomic-force microscopy, liquid chromatography–mass spectrometry, infrared spectroscopy, and Raman spectroscopy.
MS Patients and Controls Have Consistent Tear Fluid Proteome
The infrared spectroscopy of the tear fluid proteome demonstrated no significant differences between MS patients and healthy controls. The MS patients’ and controls’ spectra exhibited the three significant peaks of Amide A, Amide I, and Amide II. Hence, no tear fluid proteome changes were observed in infrared spectroscopy among MS patients.
Altered Amino Acid Profiles in Tear Fluid of MS Patients
The spectra of MS patients and controls had similar positions of peaks when the tear-fluid samples were analyzed using drop-coating deposition Raman spectroscopy. While the most intense bands reflected the vibrations of aromatic amino acid functional groups and amide bonds, the well-defined bands were associated with the vibrations of the tryptophan ring, amide group, phenylalanine ring, and tyrosine ring. Raman spectroscopy indicated a decrease in the levels of phenylalanine and tryptophan in the tear fluid samples of MS patients. ß-sheet and α-helix structures were found to be increased and decreased, respectively.
Atomic-Force Microscopy Findings
Evaluation of the surface morphology differences in the tear-fluid samples of MS patients and healthy controls revealed that the former had relatively lower roughness and different fern-shaped dendrites.
Liquid Chromatography–Mass Spectrometry Findings
The weighted gene-set and pathway enrichment analyses indicated dysregulation of MS tear-fluid proteins and lipid metabolism, respectively. The downregulated proteins in the tear-fluid samples of MS patients included haptoglobin, pre-mRNA-processing factor 17, phospholipase A2, haptoglobin, prosaposin, neutrophil gelatinase-associated lipocalin, and cytoskeletal keratin type I. The upregulated proteins included ferroptosis suppressor protein 1, cystatin C, transcobalamin-1, lactoperoxidase, phospholipid transfer protein, and immunoglobulin lambda variable 1-47.
This proteomic analysis of tear-fluid samples from MS patients and healthy controls concluded that the tear proteome in MS patients is altered and is potentially indicative of inflammation of the CNS.
Tomečková, V., Tkáčiková, S., Talian, I., Fabriciová, G., Hovan, A., Kondrakhova, D., Zakutanská, K., Skirková, M., Komanický, V., & Tomašovičová, N. (2023). Experimental Analysis of Tear Fluid and Its Processing for the Diagnosis of Multiple Sclerosis. Sensors, 23(11), 5251. https://doi.org/10.3390/s23115251