Abstract
Meibum—a lipid secretion that is produced by Meibomian glands (MG) in a process termed meibogenesis—plays a critical role in ocular surface physiology. Abnormalities in the chemical composition of meibum were linked to widespread ocular pathologies—dry eye syndrome (DES) and MG dysfunction (MGD). Importantly, in epidemiologic studies the Asian population was shown to be prone to these pathologies more than the Caucasian one, which was tied to differences in their meibomian lipids. However, biochemical data to support these observations and conclusions are limited. To determine if non-DES/non-MGD Asian meibum was significantly different from that of Caucasians, individual samples of meibum collected from ethnic Asian population living in Japan were compared with those of Caucasians living in the USA. These experiments revealed that composition of major lipid classes, such as wax esters (WE), cholesteryl esters (CE), triacylglycerols, (O)-acylated ω-hydroxy fatty acids (OAHFA), cholesteryl sulfate, cholesteryl esters of OAHFA, and diacylated α,ω-dihydroxy fatty alcohols remained invariable in both races, barring a minor (< 10%; p < 0.01) increase in the Asian CE/WE ratio. Considering the natural variability range for most meibomian lipids (app. ± 15% of the Mean), these differences in meibogenesis were deemed to be minimal and unlikely to have a measurable physiological impact.
Highlights
Meibum—a lipid secretion that is produced by Meibomian glands (MG) in a process termed meibogenesis—plays a critical role in ocular surface physiology
Note that no Caucasian volunteers were recruited for the study by Lam et al, and the conclusions were based on chemical analyses of locally collected Asian meibum samples and literature data on the Caucasian cohort, which might not be the optimal design for that study: It would be more appropriate to compare meibum lipids profiles in parallel experiments with samples of different origins, to minimize possible errors that could be introduced by differences in implemented analytical protocols
Minor presence of these contaminants in any lipid sample is virtually unavoidable as they exist in some quantities in all commercial organic solvents, but their effects were minimized during post-processing the data as described in Materials and Methods
Summary
Meibum—a lipid secretion that is produced by Meibomian glands (MG) in a process termed meibogenesis—plays a critical role in ocular surface physiology. All tested subjects were of Asian descent, and a range of major meibomian lipids, such as cholesteryl esters of ω-hydroxy fatty acids (Chl-OAHFA) and α,ω-diacylated diols (DiAD) were not detected and evaluated in either of the studies by Lam et al the lingering questions about possible differences between Asian and Caucasian meibum remained unanswered These considerations prompted us to conduct a focused study to compare intact Asian and Caucasian meibum in direct, side-by-side experiments using ultra high performance liquid chromatography and high resolution mass spectroscopy (UPLC/MS), which offer high levels of sensitivity and specificity and are the most common analytical tools for targeted and untargeted lipidomic analyses used today. Those factors will be evaluated in future projects and reported separately
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