Structure-specific tear lipid changes in dry-eye syndrome

Lipid composition of human tears elucidated and clinical implications

Dry eyes become more common as the human body ages, but previous eye surgery, heat or chemical burns, and an autoimmune condition called Sjogren syndrome can cause dry-eye syndrome.
 
In a companion paper in the Journal of Lipid Research, Sin Man Lam of the Chinese Academy of Sciences and the National University of Singapore and colleagues extracted lipids and performed mass-spectrometry analysis on samples of tears and meibum, an oily substance that prevents evaporation of tear film protecting the eye.
 
From their research, they identified novel proteins, put together a comprehensive lipidome of human tear fluid, and observed that tear fluid contains bactericidal proteins whose actions work synergistically with lipids like lysophosphatidylcholine and lysophosphatidylethanolamines that can increase neutrophil activity and have antifungal and antibacterial activity, respectively.
 
Their findings suggest tear fluid can be a future source for lipid biomarkers for systemic diseases, giving their comprehensive lipidome potential clinical relevance.

Mary L. Chang (mchang@asbmb.org) is publications manager for the Journal of Lipid Research and Molecular & Cellular Proteomics.
Stock photo of eyes
According to the American Optometric Association, most people over the age of 65 experience some symptoms of dry eyes.

People with dry-eye syndrome can experience scratchy or burning eyes, the sensation of something foreign in the eyes and blurred vision. Advanced cases may damage the front surface of the eye. Current diagnostic markers for dry-eye syndrome lack sensitivity and specificity, so researchers are seeking activity markers that align with the major axes of disease progression.
 
In light of this need, a research team with members from Singapore and China, using a comprehensive lipidomic platform, analyzed the human tear lipidome of 93 individuals to identify changes in their tear lipid compositions.
 
The patients were classified in the following clinical subgroups based on the presence of symptoms and signs: asymptomatic controls, those at risk of developing dry-eye syndrome (aqueous-deficient and nonaqueous-deficient), and symptomatic patients (aqueous-deficient and nonaqueous-deficient).
 
The team reported positive correlations between tear secretion and the levels of cholesteryl sulfates and glycosophingolipids in the tears. The researchers noted that this indicates a possible origin of these lipids in the lacrimal gland instead of the meibomian gland.
 
In addition, the researchers found that wax esters of low molecular mass and those containing saturated fatty acyl parts significantly decreased in both aqueous-deficient and nonaqueous-deficient patients. Both of these wax esters showed significant correlation with the dry-eye syndrome clinical parameter ocular surface disease index as well as with the parameters of tear breakup time and total tear secretion.
 
The study reported that these structure-specific changes in tear composition with dry-eye syndrome could be indicators of disease symptoms and signs. In addition, the authors wrote that the structure-specific alterations in tear lipids “did not reveal an actual ‘lipid-deficiency’ on the lid margins” of the dry-eye syndrome patients of subtypes with or without aqueous deficiency, but they suggested “a common pathology for both DES subtypes.”
 
Dry-eye syndrome represents one of the most frequently encountered eye diseases, particularly in older adults. It affects up to one-third of the world’s population.
 
The team’s research was published in a recent issue of the Journal of Lipid Research.

Jane CampanizziJane Campanizzi (jcmtechservices@
gmail.com) is pursuing graduate studies in the science-medical writing program at Johns Hopkins University and serves on the Publications Committee of the American Medical Writers Association.

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