This NMR study reports that meibum lipid hydrocarbon unsaturation decreases with age and is ~35% lower in cohorts with dry eye, Sjögren's syndrome, graft-versus-host disease, and Parkinson's disease compared with a non–dry-eye cohort.

Limited direct value for Parkinson's therapeutic discovery—the finding hints at peripheral lipid/tear-film changes in PD that might serve as exploratory biomarkers or prompt study of systemic lipid metabolism, but it offers no mechanistic targets or actionable therapeutic leads.

PURPOSE: The degree of unsaturation in hydrocarbon chains (HCunsat) is likely to play an important role in determining the stability, order, and fluidity of lipids in the tear film lipid layer. The HCunsat of meibum lipids was investigated in relationship with age, sex, dry eye, Sjögren's syndrome, Parkinson's disease, and treatment for allogeneic hematopoietic stem cell transplantation. METHODS: Meibum was expressed and HCunsat was measured using 1H-NMR resonances at 5.33 and 2.00 ppm. HCunsat levels were normalized to the level of wax esters, cholesteryl esters, and hydrocarbons. RESULTS: HCunsat levels, normalized to lipid esters, were found to be 20% to 40% lower in individuals aged >50 years compared with those <50 years (P < 0.05) and showed a linear age-dependent decrease with age (P < 0.001). No substantial changes were observed with sex and race, except for a 24% reduction in a small Hispanic group (P = 0.0078) compared with Caucasians. A cohort with dry eye had a ∼13% lower level of HCunsat, whereas cohorts susceptible to dry eye such as those with Sjögren's syndrome, Parkinson's, and graft-versus-host disease had a ∼35% lower HCunsat levels compared with a cohort without dry eye (P < 0.05). Experimental deviations were minimal (<4%). CONCLUSIONS: Meibum HCunsat decreases with age and is lower with dry eye, Sjögren's syndrome, and Parkinson's disease cohorts compared with a cohort without dry eye. This decrease in HCunsat is expected to contribute to lipid aggregation, decreased lipid spreading, and meibomian gland outflow. ¹H-NMR was effective for quantifying major meibum lipids.