Structural Differences in Meibum From Teenagers Without and With Dry Eye and Allogeneic Hematologic Stem Cell Transplantations

Dry eye disease in the young: A narrative review

Dry eye disease (DED), a multifactorial ocular disease that significantly impacts quality of life, is most commonly reported in adults. This review describes the prevalence, risk factors, diagnosis and management of DED in children. A literature search, conducted from January 2000-December 2022, identified 54 relevant publications. Using similar diagnostic criteria to those reported in adults, namely standardized questionnaires and evaluation of tear film homeostatic signs, the prevalence of DED in children ranged from 5.5% to 23.1 %. There was limited evidence for the influence of ethnicity in children, however some studies reported an effect of sex in older children. Factors independently associated with DED included digital device use, duration of digital device use, outdoor time and urban living, Rates of DED were higher in children with ocular allergy and underlying systemic diseases. Compared with similar studies in adults, the prevalence of a prior DED diagnosis or a diagnosis based on signs and symptoms was lower in children, but symptoms were commonly reported. Treatment options were similar to those in adults, including lifestyle modifications, blinking, management of lid disease and unpreserved lubricants in mild disease with escalating treatment with severity. Management requires careful exploration of symptoms, medical history and the diagnosis and management of ocular comorbidities such as allergy and anterior blepharitis. Appropriately powered population-based studies are required to understand the prevalence of and risk factors for DED in children. Development of age-appropriate thresholds for signs and symptoms of DED would support better diagnosis of disease and understanding of natural history.

Alteration of Meibum Lipidomics Profiling in Patients With Chronic Ocular Graft-Versus-Host Disease

Purpose

To investigate the characteristics of the lipid profiling in meibum of patients with chronic ocular graft-versus-host disease (coGVHD) and to detect the potential influence of anti-inflammatory therapy on these differential lipids.

Methods

This cross-sectional study included 25 coGVHD patients and 13 non-coGVHD after allogeneic hematopoietic stem cell transplantation. Among those with coGVHD, 14 had prior topical treatment (coGVHD(T)), and 11 did not (coGVHD(WT)). All participants completed ocular surface disease index questionnaire and received slit lamp examination, Schirmer's test without anesthesia, ocular surface interferometer, and meibography. Binocular meibum was collected and pooled for lipidomic analysis by liquid chromatography-mass spectrometry.

Results

One hundred and twenty differential lipid species were found among the three groups (96 of coGVHD(WT) vs. non-coGVHD, 78 of coGVHD(WT) vs. coGVHD(T), and three of non-coGVHD vs. coGVHD(T)). Compared with non-coGVHD group, coGVHD(WT) group had a significant abnormality of meibum composition, showing a significant decrease in glycerolipids, and an increase in glycerophospholipids and sphingolipids. Similar changes were also observed when coGVHD(WT) versus coGVHD(T). CoGVHD severity was negatively associated with mono-unsaturated triglycerides (TG), (β = -214.7; 95% CI, -363.9 to -65.5; P = 0.006) and poly-unsaturated TG (β = -4019.9; 95% CI, -7758.1 to -281.6; P = 0.036). Intensity of immunosuppression was negatively associated with mono-unsaturated TG (β = -162.4; 95% CI, -268.6 to -56.2; P = 0.004) and positively associated with phosphatidylcholine (β = 332.0; 95% CI, 19.2-644.8; P = 0.038).

Conclusions

Altered meibum in coGVHD is characterized by a decrease of glycerolipids and an increase of glycerophospholipids and may be significantly reversed by topical anti-inflammatory therapy.

A spectroscopic approach to measuring meibum lipid composition and conformation in donors with Sjӧgren's syndrome

Patients with Sjӧgren's syndrome (SS) have dry eye associated with meibomian gland dysfunction (MGD). The meibum from donors with dry eye due to MGD but without SS (MMGD) presents with lower levels of cholesteryl ester, less straight chains, and more ordered hydrocarbon chains compared with meibum from donors without MGD (Mn). The aim of the current study was to compare the composition and hydrocarbon chain conformation of meibum from donors with Sjögren's syndrome (Mss) to Mn and MMGD. Meibum was expressed from patients with SS using an ILUX instrument (Alcon Inc., Fort Worth TX). All of the nine meibum donors with SS were female. Meibum composition was characterized using 1H-NMR and meibum hydrocarbon chain conformation was measured using fourier transform infrared spectroscopy. Meibum from every donor with SS measured contained a significantly (P < 0.01) higher cholesteryl ester/wax ester ratio and more straight chains compared with donors without SS or dry eye. None of the nine phase transitional parameters were significantly different, P > 0.05, for Mss compared with Mn. Nor was the CH3/CH2 band height ratio used to estimate the number of hydrocarbon CH3 and CH2 moieties different, P = 0.22, for Mss compared with Mn. In conclusion, the compositional differences between Mss compared with Mn did not result in differences in any of the nine meibum lipid phase transitional parameters measured. The compositional differences observed between Mss and Mn could be markers for or contribute to SS as the differences could lead to tear film lipid packing differences other than conformational differences.

Meibum Lipid Composition and Conformation in Parkinsonism

PURPOSE

Patients with Parkinson's disease (PD) exhibit unstable tear films. Tear film lipid composition and structure are related to tear film stability and dry eye and tear lipids have not been characterized in people with PD. The aim of this study is to characterize Meibum tear lipids in donors with PD using ¹H-NMR and infrared spectroscopy.

METHODS

Three cohorts were compared: meibum from donors with PD (Mp) n = 10, meibum from donors with PD and dry eye (Mpd) n = 3, meibum from donors without PD (Mn) n = 29.

RESULTS

There were no significant differences, P > 0.05, in hydrocarbon branching for Mp compared with Mn. Mn contained twice as much cholesteryl esters compared with Mp, P < 0.0001. The cooperativity of the phase transition was significantly 37% lower for Mp compared with Mn, P < 0.0001. Mpd was much more ordered (stiffer) with compared with Mp and Mn, P < 0.0001.

CONCLUSION

Changes in meibum lipid composition and structure could be a marker for and/or contribute to increase the susceptibility of dry eye in patients with PD. A less cooperative phase transition for Mp compared with Mn indicates that Mp was more heterogeneous and/or contained more contaminants than Mn. The data support the idea that more ordered lipid contributes to dry eye.

Lipid conformational order and the etiology of cataract and dry eye

Lens and tear film lipids are as unique as the systems they reside in. The major lipid of the human lens is dihydrosphingomylein, found in quantity only in the lens. The lens contains a cholesterol to phospholipid molar ratio as high as 10:1, more than anywhere else in the body. Lens lipids contribute to maintaining lens clarity, and alterations in lens lipid composition due to age are likely to contribute to cataract. Lens lipid composition reflects adaptations to the unique characteristics of the lens: no turnover of lens lipids or proteins; the lowest amount of oxygen of any tissue; and contains almost no intracellular organelles. The tear film lipid layer (TFLL) is also unique. The TFLL is a thin (100 nm) layer of lipid on the surface of tears covering the cornea that contributes to tear film stability. The major lipids of the TFLL are wax esters and cholesterol esters that are not found in the lens. The hydrocarbon chains associated with the esters are longer than those found anywhere else in the body (as long as 32 carbons), and many are branched. Changes in the composition and structure of the 30,000 different moieties of TFLL contribute to the instability of tears. The focus of the current review is how spectroscopy has been used to elucidate the relationships between lipid composition, conformational order and function, and the etiology of cataract and dry eye.

Meibum lipid hydrocarbon chain branching and rheology after hematopoietic stem cell transplantation

Purpose

Meibum from donors who have had hematological stem cell transplantations (M_HSCT) are susceptible to severe dry eye symptoms and exhibit very high lipid order (stiffness) compared with meibum from donors without dry eye (M_n). Since lipid order could have functional consequences, we compared the rheology and composition of M_n and M_HSCT to measure meibum compositional, structural and functional relationships.

Methods

The rheology and composition was measured using Langmuir trough and ¹H NMR spectroscopy, respectively.

Results

M_HSCT and M_n was studied from 16 to 43 donors, respectively, using NMR spectroscopy. M_HSCT contained significantly 16% more straight chain and 24% less iso-chain hydrocarbons compared with M_n. The cholesteryl ester to wax ester molar ratio, and hydrocarbon chain unsaturation were not significantly different, for M_HSCT compared with M_n.

Surface pressure-area isotherms of meibum from 30 donors without dry-eye were grouped into 4 pools (PC) and meibum from 32 donors with dry eye who had hematopoietic stem cell transplantation (PT) were grouped into 3 pools. Above 15 years of age the П_max and (C_s⁻¹)_max increased with age for both the PC and the PT cohorts. (C_s⁻¹)_max values were higher for PT samples compared with age matched PC samples, indicating they had higher elasticity and stiffness. A more ordered lipid could contribute to the formation of a discontinuous patchy tear film lipid layer, which in turn results in deteriorated spreading, and decreased surface elasticity.

Conclusions

The composition and rheology of meibum from donors with dry eye and who have had HSCT support the idea from other studies that more ordered meibum may contribute to or be a marker of dry eye.

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More straight chain and less iso-chain hydrocarbons could contribute to HSCT dry eye.

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Meibum elasticity and stiffness increased with age.

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Meibum elasticity and stiffness increased with HSCT dry eye.

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Differences could contribute to a discontinuous patchy tear film lipid layer.

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Differences could result in deteriorated spreading, and decreased surface elasticity.

Lipid Saturation and the Rheology of Human Tear Lipids

Elevated levels of acyl chain saturation of meibomian lipids are associated with enhanced tear film (TF) stability in infants to shortened TF breakup time with meibomian gland dysfunction. Thus, the effect of saturation on the surface properties of human TF lipids (TFLs) using a Langmuir surface balance and Brewster angle microscopy was studied. Lipid phase transitions were measured using infrared spectroscopy. The raise in the % of saturation resulted in thicker, and more elastic films at π = 12 mN/m, with the effects being proportional to the saturation level. At the same time, at lower (≤10 mN/m) π, the raise in saturation resulted in an altered spreading and modified structure of TFL layers. The strong impact of saturation on TFL surface properties correlated with a saturation induced increase of the TFL acyl chain order, phase transition temperature, and lipid-lipid interactions. The native TFL order and π_max were significantly greater, compared with native meibum collected from the same individual. Aggregation of lipids on the tear surface due to saturation was not as significant as it was for meibum. Although the surface pressure/area isotherms for TFL were similar for meibum, differences in rheology and phase transition parameters warrant the study of both.