Quantification of Human Sebum on Skin and Human Meibum on the Eye Lid Margin Using Sebutape®, Spectroscopy and Chemical Analysis

Relationship Between Human Meibum Lipid Composition and the Severity of Meibomian Gland Dysfunction: A Spectroscopic Analysis

Purpose

Information on the relationship between meibum lipid composition and severity of meibomian gland dysfunction (MGD) is limited. The purpose of this study was to analyze the molecular components of meibum collected from individuals with no MGD, mild-to-moderate MGD, and severe MGD.

Methods

Adults with and without MGD were enrolled in a prospective, multicenter, exploratory clinical trial (ClinicalTrials.gov Identifier: NCT01979887). Molar ratios of cholesteryl ester to wax ester (RCE/WE) and aldehyde to wax ester (Rald/WE) in meibum samples were measured with 1H-NMR spectroscopy. Results were evaluated for participants grouped by MGD disease status and severity (non-MGD, mild-to-moderate MGD, and severe MGD), as defined by maximum meibum quality scores, Schirmer test results, and Subject Ocular Symptom Questionnaire responses.

Results

Sixty-nine meibum samples from 69 individuals were included in the analysis: 24 non-MGD, 24 mild-to-moderate MGD, and 21 severe MGD. Mean RCE/WE was 0.29 in non-MGD, 0.14 in mild-to-moderate MGD (P = 0.038 vs. non-MGD, 51% lower), and 0.07 in severe MGD (P = 0.16 vs. mild-to-moderate MGD, 52% lower; P = 0.002 vs. non-MGD, 76% lower). Mean Rald/WE was 0.00022 in non-MGD, 0.00083 in mild-to-moderate MGD (P = 0.07 vs. non-MGD, 277% higher), and 0.0024 in severe MGD (P = 0.003 vs. mild-to-moderate MGD, 190% higher; P < 0.001 vs. non-MGD, 992% higher).

Conclusions

RCE/WE was lowest and Rald/WE was highest in the severe MGD cohort, suggesting that these meibum constituent molar ratios may result from the pathophysiology associated with MGD and can impact ocular surface lipid and tear film homeostasis. These findings may potentially help identify targets for MGD treatment.

Candidate Molecular Compounds as Potential Indicators for Meibomian Gland Dysfunction

Meibomian gland dysfunction (MGD) is the leading cause of dry eye disease throughout the world. Studies have shown that several molecules in meibum, including but not limited to interleukins, amino acids, cadherins, eicosanoids, carbohydrates, and proteins, are altered in meibomian gland dysfunction compared with healthy normal controls. Some of these molecules such as antileukoproteinase, phospholipase A2, and lactoperoxidase also show differences in concentrations in tears between meibomian gland dysfunction and dry eye disease, further boosting hopes as candidate biomarkers. MGD is a complex condition, making it difficult to distinguish patients using single biomarkers. Therefore, multiple biomarkers forming a multiplex panel may be required. This review aims to describe molecules comprising lipids, proteins, and carbohydrates with the potential of serving various capacities as monitoring, predictive, diagnostic, and risk biomarkers for meibomian gland dysfunction.

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.

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.

Changes in meibum composition following plaque bachytherapy for choroidal melanoma

Objectives

Dry eye is common when external beam radiation is used for the treatment of choroidal melanoma (CM). As meibum structure and composition have been related to dry eye, we determined if plaque bachytherapy for CM alters meibum composition.

Design

¹H-NMR spectroscopy was used to measure the lipid composition of meibum.

Setting

The University of Louisville, Kentucky, USA.

Participants

All 13 participants had CM and one participant had iris melanoma.

Main outcome measures

Cholesteryl ester (CE) to wax ester (WE) ratio, amount of meibum esters (ME) and meibum lipid saturation were measured.

Results

ME decreased by 80%±18% (±99% CI) in 11 eyes that were treated compared with the contralateral untreated eye. ME increased by 181% in two eyes that were treated compared with the contralateral untreated eye. The mole % CE/WE for meibum was significantly (p<0.0001) 67% lower in eyes that were irradiated compared with control eyes from donors without CM and were not treated. Plaque brachytherapy induced the de-esterification of CE. The intensity of the meibum cis double bond resonances did not change significantly (p>0.05).

Conclusion

Eyes that had plaque brachytherapy had a lower amount of expressible meibum and a lower CE/WE ratio compared with meibum from the contralateral eye that received no treatment and eyes that did not have uveal melanoma. Both the quality and quantity of meibum should be considered in designing a therapy for dry eye after plaque brachytherapy.

Handheld swept-source optical coherence tomography guided by smartphone-enabled wide-field autofluorescence photography for imaging facial sebaceous glands

We report a method to image facial sebaceous glands (SGs) using smartphone-enabled wide-field autofluorescence photography (AFP) and handheld swept-source optical coherence tomography (SS-OCT). Smartphone-enabled AFP provides a 2D wide-field fluorescence image that is used both as a functional mapping of the sebum and a positioning guidance for OCT imaging of the SG. Following the guidance, handheld SS-OCT conducts the volume scan to investigate depth-resolved conditions of the SG in the selected regions of interest. We show the results from smartphone-enabled AFP and handheld SS-OCT to demonstrate the ability of our method to image facial SGs, potentially useful for the assessment of skin conditions in dermatology and cosmetology.

New method for large-scale facial skin sebum quantification and skin type classification

BACKGROUND

The demand for personalized skin care is increasing rapidly in recent years. In order to provide suitable products for different customers, an accurate assessment of the skin condition is required. It is necessary to establish a remote and convenient method for quantifying skin condition.

MATERIALS AND METHODS

We established a new method for quantifying the facial sebum excretion, using Sebutape as well as a model for objective skin type classification.

RESULTS

In total, 2173 sebum quantification samples were collected and categorized into 4 skin types. We found good agreement between subjective and objective skin types. 60.33% of the detection is consistent, and the proportion of discrepancies is only 0.55%. The main mismatch is caused by broad criteria for combination type classification. Quantifying the sebum excretion will help to describe and analyze the skin state easily. We found sebum levels in Chinese women peak at the age between 20 and 30 and decrease dramatically after age 40s.

CONCLUSION

This new sebum quantitative method is well consistent to self-report skin type. In addition, it provides a powerful tool for the cosmetic industry to evaluate skin condition precisely and recommend personalized products accordingly.

Human sebum requires de novo lipogenesis, which is increased in acne vulgaris and suppressed by acetyl-CoA carboxylase inhibition

Sebum plays important physiological roles in human skin. Excess sebum production contributes to the pathogenesis of acne vulgaris, and suppression of sebum production reduces acne incidence and severity. We demonstrate that sebum production in humans depends on local flux through the de novo lipogenesis (DNL) pathway within the sebocyte. About 80 to 85% of sebum palmitate (16:0) and sapienate (16:1n10) were derived from DNL, based on stable isotope labeling, much higher than the contribution of DNL to triglyceride palmitate in circulation (~20%), indicating a minor contribution by nonskin sources to sebum lipids. This dependence on local sebocyte DNL was not recapitulated in two widely used animal models of sebum production, Syrian hamsters and Göttingen minipigs. Confirming the importance of DNL for human sebum production, an acetyl-CoA carboxylase inhibitor, ACCi-1, dose-dependently suppressed DNL and blocked synthesis of fatty acids, triglycerides, and wax esters but not free sterols in human sebocytes in vitro. ACCi-1 dose-dependently suppressed facial sebum excretion by ~50% (placebo adjusted) in human individuals dosed orally for 2 weeks. Sebum triglycerides, wax esters, and free fatty acids were suppressed by ~66%, whereas non-DNL-dependent lipid species, cholesterol, and squalene were not reduced, confirming selective modulation of DNL-dependent lipids. Last, individuals with acne vulgaris exhibited increased sebum production rates relative to individuals with normal skin, with >80% of palmitate and sapienate derived from DNL. These findings highlight the importance of local sebocyte DNL for human skin sebaceous gland biology and illuminate a potentially exploitable therapeutic target for the treatment of acne vulgaris.

Clinical results of Intraductal Meibomian gland probing combined with intense pulsed light in treating patients with refractory obstructive Meibomian gland dysfunction: a randomized controlled trial

Background

This study aims to optimize the therapeutic regimen for refractory obstructive meibomian gland dysfunction (o-MGD) patients by combining intraductal meibomian gland probing (MGP) and intense pulsed light (IPL) to enhance their positive effects and reduce their limitations.

Methods

This randomized, assessor blind study includes 45 patients (90 eyes) with refractory o-MGD who were divided into 3 groups via allocation concealment: IPL (group I, received an IPL treatment course: 3 times at 3-week intervals), MGP (group II, received MGP one time), and combined MGP-IPL (group III, MGP first followed by an IPL treatment course). Standard Patient Evaluation of Eye Dryness score (SPEED), tear break-up time (TBUT), corneal fluorescein staining (CFS), meibum grade, and lid margin finding results were assessed at baseline, 3 weeks after final treatment for groups I and III, 3 and 12 weeks after MGP for group II. Six months after final treatment, the SPEED and willingness to receive any treatment again were also collected for all groups. Paired Wilcoxon, Mann-Whitney U with Bonferroni correction, and Kruskal-Wallis tests were used for data analysis.

Results

For all 3 groups, all previously mentioned indexes improved significantly following treatment (P<0.01). MGP-IPL was better than IPL and MGP in terms of post-treatment SPEED, TBUT, meibum grade, and lid telangiectasia (P<0.05/3). Furthermore, the MGP-IPL was better than IPL in terms of lid tenderness and better than MGP in terms of orifice abnormality (P< 0.05/3). Six months later, the SPEED for the MGP-IPL was also significantly lower than other groups (P<0.05/3). Moreover, no patients in the MGP-IPL group expressed the need to be treated again compared to 35.7% or 20% of patients in the IPL or MGP groups, respectively.

Conclusions

Compared with IPL or MGP alone, the combination MGP-IPL produced best results in relieving all signs and symptoms and helping patients attain long-lasting symptom relief.

Trial registration

http://clinicaltrials.gov, ChiCTR1900021273 (retrospectively registered February 9, 2019).

Histopathology and selective biomarker expression in human meibomian glands

Background/aims

Meibomian gland dysfunction (MGD) is the most common form of evaporative dry eye disease, but its pathogenesis is poorly understood. This study examined the histopathological features of meibomian gland (MG) tissue from cadaver donors to identify potential pathogenic processes that underlie MGD in humans.

Methods

Histological analyses was performed on the MGs in the tarsal plates dissected from four cadaver donors, two young and two old adults, including a 36-year-old female (36F) and three males aged 30, 63 and 64 years (30M, 63M and 64M).

Results

The MGs of 36F displayed normal anatomy and structure, whereas the MGs of 30M showed severe ductal obstruction with mild distortion. The obstruction was caused by increased cytokeratin levels in association with hyperproliferation, but not hyperkeratinisation. In two older males, moderate to severe MG atrophy was noted. Cell proliferation was significantly reduced in the MG acini of the two older donors as measured by Ki67 labelling index (6.0%±3.4% and 7.9%±2.8% in 63M and 64M, respectively) when compared with that of the two younger donors (23.2%±5.5% and 16.9%±4.8% in 30M and 36F, respectively) (p<0.001). The expression patterns of meibocyte differentiation biomarkers were similar in the older and younger donors.

Conclusion

Our histopathological study, based on a small sample size, suggests potentially distinct pathogenic mechanisms in MGD. In the young male adult, hyperproliferation and aberrant differentiation of the central ductal epithelia may lead to the obstruction by overproduced cytokeratins. In contrast, in older adults, decreased cell proliferation in acinar basal epithelia could be a contributing factor leading to MG glandular atrophy.

Structural Differences in Meibum From Donors After Hematopoietic Stem Cell Transplantations

PURPOSE

Meibum is considered to be a key component of tears that serve to protect the eye, and conformational changes in meibum have not been studied extensively within the population of patients who had hematopoietic stem cell transplantation (HSCT). The aim of this study was to determine possible lipid conformational changes in the meibum of patients who had HSCT.

METHODS

Participants who had HSCT were randomly sampled for this prospective comparative study. Control participants did not have dry eye or had not undergone allogeneic or autologous stem cell transplantation. Fourier-transform infrared spectroscopy was used to measure meibum phase transition.

RESULTS

Meibum was collected from both eyes of 36 donors without dry eye (Mc) and from 22 patients who had undergone HSCT (MHSCT). There were no significant differences between the phase transition parameters based on gender or race. The following were the significant differences (P < 0.0001) between the parameters for Mc compared with MHSCT : lipid order (% trans) at 33.4°C increased from 40 (1) to 54 (2), cooperativity decreased from 7.9 (0.4) to 5.4 (0.3), the phase transition temperature (C) increased from 30.3 (0.4) to 34.2 (0.9), and the magnitude of the phase transition (cm) increased from 4.0 (0.1) to 4.7 (0.5) (standard error of the mean).

CONCLUSIONS

Conformational and thermodynamic differences were observed between Mc and MHSCT. The changes observed in the lipid conformation of meibum from patients receiving HSCTs suggest that meibum composition changes after stem cell transplantation, and clinicians should consider treating the meibomian glands to improve the ocular surface.

Insights into Tear Film Stability from Babies and Young Adults: A Study of Human Meibum Lipid Conformation and Rheology

Babies have the most stable tears and people with dry eye have the least stable tears. Meibum may contribute to tear film stability, so in this study, the hydrocarbon chain conformation and rheology of meibum from babies was studied for the first time. Infrared spectroscopy was used to measure lipid phase transitions. Rheology was measured using Langmuir film technology. Meibum from 25 donors 1 to 13 years old was compared with meibum from 18 donors 13 to 25 years old. The phase transition temperature and lipid order (stiffness) increased with increasing age from 1 to 25 years. The increase in meibum lipid order from 1 to 25 years of age may contribute to the instability of the tear film with age and contribute to films with a higher reciprocal compressibility modulus that are not as compressible and not as viscoelastic. Changes in the lipid phase transition parameters of meibum lipid with dry eye are an exacerbation of the changes observed with age. The lower reciprocal compressibility moduli of meibum films from children and babies compared with meibum from adults reiterates higher stability in their films which spread better, resist deformation, and facilitates their ability to be quickly restored after blinking.

Sebum/Meibum Surface Film Interactions and Phase Transitional Differences

Purpose

Sebum may contribute to the composition of the tear film lipid layer naturally or as a contaminant artifact from collection. The aims of this study were to determine: if sebum changes the rheology of meibum surface films; if the resonance near 5.2 ppm in the ¹H-NMR spectra of sebum is due to squalene (SQ); and if sebum or SQ, a major component of sebum, interacts with human meibum.

Methods

Human meibum was collected from the lid margin with a platinum spatula. Human sebum was collected using lipid absorbent tape. Langmuir trough technology was used to measure the rheology of surface films. Infrared spectroscopy was used to measure lipid conformation and phase transitions. We used ¹H-NMR to measure composition and confirm the primary structure of SQ.

Results

The NMR resonance near 5.2 ppm in the spectra of human sebum was from SQ which composed 28 mole percent of sebum. Both sebum and SQ lowered the lipid order of meibum. Sebum expanded meibum films at lower concentrations and condensed meibum films at higher concentrations. Sebum caused meibum to be more stable at higher pressures (greater maximum surface pressure).

Conclusions

Physiological levels of sebum would be expected to expand or fluidize meibum making it spread better and be more surface active (qualities beneficial for tear film stability). Sebum would also be expected to stabilize the tear film lipid layer, which may allow it to withstand the high shear pressure of a blink.

Efficacy of Intraductal Meibomian Gland Probing on Tear Function in Patients With Obstructive Meibomian Gland Dysfunction

PURPOSE

To assess the efficacy and safety of intraductal meibomian gland probing in patients with obstructive meibomian gland dysfunction who experienced little improvement with eyelid warming, massage, or artificial tears.

METHODS

Forty-nine patients with obstructive meibomian gland dysfunction were randomly divided into 2 groups: intraductal meibomian gland probing with 0.1% fluorometholone (group I), and 0.1% fluorometholone alone (group II). Subjective symptom scores and objective signs, including lid margin abnormalities, meibum quality and expressibility, meibomian gland dropout, fluorescein staining, tear break-up time (TBUT), and Schirmer I test results, were recorded before treatment and after 1 day, 1 week, and 1 month posttreatment.

RESULTS

Clinical subjective symptoms and objective signs including meibum grade, TBUT, lid margin abnormalities, and fluorescein staining demonstrated significant improvements in both groups after treatment over time (all P < 0.05), and group I was better than group II 1 month after treatment in meibum grade (6.1 ± 3.3 vs. 10.4 ± 4.9, respectively; P < 0.001), lid margin abnormalities (0.8 ± 0.1 vs. 1.3 ± 0.3, respectively; P < 0.001), and TBUT (8.2 ± 2.1 vs. 7.0 ± 3.0, respectively; P = 0.0293). Before applying any medications, 76% of patients obtained immediate symptom relief 1 day after probing. However, the Schirmer I test results and meibomian gland dropout were insignificant pre- and posttreatment in either group (P > 0.1, respectively).

CONCLUSIONS

Intraductal meibomian gland probing demonstrated significant efficacy in symptom relief and tear film stabilization. Probing helped release accumulated meibum and could help increase the accessibility of diseased meibomian glands to topical corticosteroids.

Dissecting lipid metabolism in meibomian glands of humans and mice: An integrative study reveals a network of metabolic reactions not duplicated in other tissues

Lipids comprise the bulk of the meibomian gland secretion (meibum) which is produced by meibocytes. Complex arrays of lipogenic reactions in meibomian glands, which we collectively call meibogenesis, have not been explored on a molecular level yet. Our goals were to elucidate the possible biosynthetic pathways that underlie the generation of meibum, reveal similarities in, and differences between, lipid metabolism in meibomian glands and other organs and tissues, and integrate meibomian gland studies into the field of general metabolomics. Specifically, we have conducted detailed analyses of human and mouse specimens using genomic, immunohistochemical, and lipidomic approaches. Among equally highly expressed genes found in meibomian glands of both species were those related to fatty acid elongation, branching, desaturation, esterification, reduction of fatty acids to alcohols, and cholesterol biosynthesis. Importantly, corresponding lipid products were detected in meibum of both species using lipidomic approaches. For the first time, a cohesive, unifying biosynthetic scheme that connects genomic, lipidomic, and immunohistochemical observations is outlined and discussed.

Surface Properties of Squalene/Meibum Films and NMR Confirmation of Squalene in Tears

Squalene (SQ) possesses a wide range of pharmacological activities (antioxidant, drug carrier, detoxifier, hydrating, emollient) that can be of benefit to the ocular surface. It can come in contact with human meibum (hMGS; the most abundant component of the tear film lipid layer) as an endogenous tear lipid or from exogenous sources as eyelid sebum or pharmaceuticals. The aims of this study were to determine (i) if SQ is in tear lipids and (ii) its influence on the surface properties of hMGS films. Heteronuclear single quantum correlation NMR confirmed 7 mol % SQ in Schirmer’s strips extracts. The properties of SQ/hMGS pseudo-binary films at the air/water interface were studied with Langmuir surface balance, stress-relaxation dilatational rheology and Brewster angle microscopy. SQ does not possess surfactant properties. When mixed with hMGS squalene (i) localized over the layers’ thinner regions and (ii) did not affect the film pressure at high compression. Therefore, tear SQ is unlikely to instigate dry eye, and SQ can be used as a safe and “inert” ingredient in formulations to protect against dry eye. The layering of SQ over the thinner film regions in addition to its pharmacological properties could contribute to the protection of the ocular surface.

Comparison of meibomian gland loss and expressed meibum grade between the upper and lower eyelids in patients with obstructive meibomian gland dysfunction

PURPOSE

The aim of this study was to compare meibomian gland loss (MGL) and expressed meibum grade between upper and lower eyelids in patients with obstructive meibomian gland dysfunction (MGD) and to evaluate the correlation between these 2 parameters and other clinical measurements.

METHODS

Twenty-six eyes of 26 patients with obstructive MGD were enrolled. Upper and lower MGLs were evaluated using noncontact meibography. Expressed meibum quality was assessed in 8 glands of the central third area of the upper and lower eyelids on a scale of 0 to 3 for each gland (total score range, 0-24). Tear film stability was evaluated based on tear break-up time (TBUT), and corneal staining was graded according to the National Eye Institute scale (range, 0-15).

RESULTS

The mean MGL in the lower eyelids (24.1% ± 10.8%) was significantly greater than that of the upper eyelids (11.2% ± 5.2%) (P < 0.001). The mean expressed meibum grade in the lower eyelids (16.5 ± 5.1) was also significantly larger than that of the upper eyelids (11.2 ± 5.2) (P < 0.001). MGL was significantly correlated with expressed meibum grade in both eyelids (r = 0.451, P = 0.021 in the upper eyelids; r = 0.626, P = 0.001 in the lower eyelids). The meibum grades of both the upper and lower eyelids were negatively correlated with TBUT and positively correlated with corneal staining score. However, the MGL in both the eyelids was not correlated with TBUT or with corneal staining score.

CONCLUSIONS

In patients with obstructive MGD, MGL and meibum grade in the lower eyelids were significantly greater than those of the upper eyelids. Although MGL and meibum quality showed a positive correlation with each other, TBUT and corneal staining score were significantly correlated with only meibum grade, and not with MGL.

Effect of desiccating stress on mouse meibomian gland function

PURPOSE

Mice exposed to standardized desiccating environmental stress to induce dry eye-like symptoms have been used as a model to study the underlying mechanisms of evaporative dry eye. While studies have shown marked inflammatory and immune changes, the effect of such stress on meibomian gland function remains largely unknown. We sought to evaluate the effects of desiccating stress on meibocyte proliferation and meibum quality.

METHODS

Ten mice were treated with scopolamine and subjected to a drafty low humidity environment (30-35%). Five and ten days after treatment, eyelids were harvested and cryosections stained with Ki67 antibody to identify cycling cells. Sections were also imaged using stimulated Raman scattering (SRS) microscopy to characterize the gland compositional changes by detecting the vibrational signatures of methylene (lipid) and amide-I (protein).

RESULTS

Desiccating stress caused a 3-fold increase in basal acinar cell proliferation from 18.3 ± 11.1% in untreated mice to 64.4 ± 19.9% and 66.6 ± 13.4% after 5 and 10 days exposure, respectively (P < .001). In addition, SRS analysis showed a wider variation in the protein-to-lipid ratio throughout the gland, suggesting alterations in meibocyte differentiation and lipid synthesis.

CONCLUSIONS

These data are consistent with a model that a desiccating environment may have a direct effect on meibomian gland function, leading to a significant increase in basal acinar cell proliferation, abnormal meibocyte differentiation, and altered lipid production.

Topical azithromycin and oral doxycycline therapy of meibomian gland dysfunction: a comparative clinical and spectroscopic pilot study

PURPOSE

Meibomian gland dysfunction (MGD) is a common clinical problem that is often associated with evaporative dry eye disease. Alterations of the lipids of the meibomian glands have been identified in several studies of MGD. This prospective, observational, open-label clinical trial documents the improvement in both clinical signs and symptoms of disease as well as spectroscopic characteristics of the meibomian gland lipids after therapy with topical azithromycin ophthalmic solution and oral doxycycline treatment.

METHODS

Subjects with symptomatic MGD were recruited. Signs of MGD were evaluated with a slit lamp. Symptoms of MGD were measured by the response of subjects to a questionnaire. Meibum lipid-lipid interaction strength, conformation, and phase transition parameters, and meibum protein content were measured using Fourier transform infrared spectroscopy and principal component analysis. Terpenoids, short-chain CH3 moieties, lipid oxidation, wax, cholesterylesters and glycerides were measured with a proton nuclear magnetic resonance (H-NMR) spectrometer.

RESULTS

Topical therapy with azithromycin and oral therapy with doxycycline relieved signs and symptoms and restored the lipid properties of the meibomian gland secretion toward normal. Compared with 4 weeks of azithromycin treatment reported in our previous study, oral doxycycline treatment was slightly less effective in improving foreign body sensation and the signs of plugging and secretion. In subjects with clinical evidence of MGD, changes in ordering of the lipids and phase transition temperature were brought closer to normal with azithromycin treatment than doxycycline treatment. Treatment with doxycycline but not azithromycin restored the Fourier transform infrared spectroscopy-principal component analysis scores and relative area of the H-NMR resonance at 1.26 ppm. Both doxycycline and azithromycin treatment restored the levels of the relative areas of the H-NMR resonance at 5.2 and 7.9 ppm to normal levels. The levels of meibum protein and meibum lipid oxidation were not influenced by azithromycin or doxycycline treatment.

CONCLUSIONS

The mechanism of action of doxycycline may be different from that of azithromycin in therapy of MGD. It is notable that when carotenoids in meibum are low, as in MGD, the tear film is unstable and patients have the signs and symptoms of dry eyes. When carotenoids are restored with azithromycin and doxycycline treatment, tear film stability is restored and patients no longer have the signs and symptoms of dry eyes.

Wakayama Symposium: Peroxisome proliferator-activated receptor-gamma (PPARγ) and meibomian gland dysfunction

Recently we have shown that mouse and human meibomian glands undergo specific age-related changes, including decreased acinar cell proliferation, acinar atrophy, and altered peroxisome proliferator-activated receptor gamma (PPARγ) localization from cytoplasmic-vesicular/nuclear in young mice and humans to nuclear in old mice and humans. Since PPARγ is a lipid-sensitive, nuclear receptor implicated in regulating adipocyte and sebocyte differentiation and lipogenesis, our findings suggest that PPARγ may be involved in modulating meibomian gland differentiation during aging. Based on these findings, we propose that aging of the meibomian gland results in downregulation of PPARγ, leading to decreased meibocyte differentiation and lipid synthesis, gland atrophy, and a hyposecretory meibomian gland dysfunction.

Wax-tear and meibum protein, wax-β-carotene interactions in vitro using infrared spectroscopy

Protein-meibum and terpenoids-meibum lipid interactions could be important in the etiology of meibomian gland dysfunction (MGD) and dry eye symptoms. In the current model studies, attenuated total reflectance (ATR) infrared (IR) spectroscopy was used to determine if the terpenoid β-carotene and the major proteins in tears and meibum affect the hydrocarbon chain conformation and carbonyl environment of wax, an abundant component of meibum. The main finding of these studies is that mucin binding to wax disordered slightly the conformation of the hydrocarbon chains of wax and caused the wax carbonyls to become hydrogen bonded or experience a more hydrophilic environment. Lysozyme and lactoglobulin, two proteins shown to bind to monolayers of meibum, did not have such an effect. Keratin and β-carotene did not affect the fluidity (viscosity) or environment of the carbonyl moieties of wax. Based on these results, tetraterpenoids are not likely to influence the structure of meibum in the meibomian glands. In addition, these findings suggest that it is unlikely that keratin blocks meibomian glands by causing the meibum to become more viscous. Among the tear fluid proteins studied, mucin is the most likely to influence the conformation and carbonyl environment of meibum at the tear film surface.

Changes in human meibum lipid composition with age using nuclear magnetic resonance spectroscopy

PURPOSE

Human tear film stability decreases with increasing age. In this study, the changes in meibum composition were measured in search of markers of tear film instability.

METHODS

(1)H NMR nuclear magnetic resonance (NMR) spectra of 43 normal donors aged 1 to 88 years were acquired.

RESULTS

Compared with meibum from adolescents and adults, meibum from infants and children contains less CH(3) and C═C groups and an increased aldehyde-to-lipid hydroperoxide ratio.

CONCLUSIONS

It is reasonable that tear film stability is higher in infants than in adults. Their meibum contains less CH(3) and C═C groups and higher levels of protein, and as a result, the lipid is more ordered because of the tighter and stronger lipid-lipid interactions. For water to evaporate, it must first pass through the tight lipid-lipid barrier. For tears to break up, lipid-lipid interactions must be broken. It is reasonable that because the lipid-lipid interactions are stronger in infants' and children's tears compared with those of adolescents and adults, the tear film in the younger groups is more stable and provides a better barrier to evaporation than does the tear film of adults. Lipid saturation could be the critical feature in meibum that stabilizes tears in infants.

Differences in human meibum lipid composition with meibomian gland dysfunction using NMR and principal component analysis

PURPOSE

Nuclear magnetic resonance (NMR) spectroscopy has been used to quantify lipid wax, cholesterol ester terpenoid and glyceride composition, saturation, oxidation, and CH₂ and CH₃ moiety distribution. This tool was used to measure changes in human meibum composition with meibomian gland dysfunction (MGD).

METHODS

(1)H-NMR spectra of meibum from 39 donors with meibomian gland dysfunction (Md) were compared to meibum from 33 normal donors (Mn).

RESULTS

Principal component analysis (PCA) was applied to the CH₂/CH₃ regions of a set of training NMR spectra of human meibum. PCA discriminated between Mn and Md with an accuracy of 86%. There was a bias toward more accurately predicting normal samples (92%) compared with predicting MGD samples (78%). When the NMR spectra of Md were compared with those of Mn, three statistically significant decreases were observed in the relative amounts of CH₃ moieties at 1.26 ppm, the products of lipid oxidation above 7 ppm, and the =CH moieties at 5.2 ppm associated with terpenoids.

CONCLUSIONS

Loss of the terpenoids could be deleterious to meibum since they exhibit a plethora of mostly positive biological functions and could account for the lower level of cholesterol esters observed in Md compared with Mn. All three changes could account for the higher degree of lipid order of Md compared with age-matched Mn. In addition to the power of NMR spectroscopy to detect differences in the composition of meibum, it is promising that NMR can be used as a diagnostic tool.

Analysis of the composition of lipid in human meibum from normal infants, children, adolescents, adults, and adults with meibomian gland dysfunction using ¹H-NMR spectroscopy

PURPOSE

This study represents a first step toward the evaluation of possible compositional differences in meibum from normal donors (Mn) and donors with meibomian gland dysfunction (Md) by (1)H-NMR spectroscopy. The results highlight the applicability of (1)H-NMR spectroscopy for the quantitative analysis of waxes, cholesteryl esters, and glycerides in meibum lipid (ML).

METHODS

Meibum was obtained from 41 normal donors and 51 donors with meibomian gland dysfunction (MGD). (1)H-NMR spectroscopy was used to quantify the amount of waxes, glycerides, and cholesteryl esters in human meibum.

RESULTS

The relative amount of cholesteryl esters in Mn increased with age and was 40% (P < 0.05) lower in Md. Interestingly, the relative levels of cholesteryl esters in infant meibum were comparable to those in Md. The relative amounts of glycerides were not affected significantly by age or MGD.

CONCLUSIONS

The changes in cholesteryl ester could be used as a molecular marker for MGD and could potentially be applied to follow the efficacy of drug therapy in the treatment of MGD. The similarity of the levels of cholesteryl esters in infant meibum and Md suggests that the relative amounts of these meibum components alone are unlikely to be responsible for the increased stability of the infant tear film and decreased stability of the tear film with MGD. This study reveals the complexity of human MLs and the changes that occur with age and disease. Understanding the factors that lead to such variations is of utmost relevance in the design of effective therapies.