RESUMEN
PURPOSE: The effect of skin lipids on the formation and stability of the human tear film was investigated. METHODS: Skin swab substances (SSSs) were applied to the eyes of volunteers and studied using fluorescein or with TearView, which records infrared emissivity showing tear film integrity in real time. Results were compared with similar experiments using castor oil, freshly collected meibum, or acetic acid, which simulated the low pH of the skin. RESULTS: Fluorescein and TearView results were comparable. TearView showed the natural unaltered tear film over the whole eye, instant changes to the tear film, and meibomian gland activity. Minimal amounts of SSS destroyed the integrity of the film and caused pain. Corneal epithelial damage could be detected. TearView showed that SSS stimulated meibomian gland secretion if applied directly to the posterior eyelid margin. Excess meibum had no effect on the tear film spread or integrity. Castor oil formed floating lenses on the tear film which were spread by a blink but then condensed back toward themselves. There was no pain or surface damage with these oils. CONCLUSIONS: SSS contamination of the ocular surface disrupts the tear film, causes stinging, and fluorescein staining of the corneal epithelial cells after a blink. SSS stimulates meibomian gland activity. It is possible that various ocular conditions associated with dry eye, such as blepharitis and ocular rosacea, may compromise a meibomian lipid barrier of the eye lid margin. Skin lipids would then have access to the ocular surface and cause dry eye symptoms.
Asunto(s)
Síndromes de Ojo Seco , Laceraciones , Humanos , Lágrimas/química , Aceite de Ricino/análisis , Aceite de Ricino/farmacología , Glándulas Tarsales , Síndromes de Ojo Seco/etiología , Fluoresceína/farmacologíaRESUMEN
PURPOSE: This study was to establish a controlled in vitro test system to study the effect of lipid oxidation on lipid deposition on contact lenses. METHODS: Fatty acids with varying degree of unsaturation were oxidized using the Fenton reaction. The degree of lipid oxidation and the lipid moieties formed during the oxidation were identified and estimated by various lipid staining techniques following separation with thin-layer chromatography, and by measuring thiobarbituric acid reactive substances or peroxides in solution. Two different silicone hydrogel-based contact lenses (Balafilcon A and Senofilcon A) were incubated with fatty acids laced with radioactive tracer oxidized to varying degrees, and the amount of lipid deposition was measured using unoxidized lipid samples as controls. RESULTS: The Fenton reaction together with the analytical methods to analyze the lipid oxidation can be used to control oxidation of lipids to a desired amount. In general, saturated fatty acids are not oxidized, the monounsaturated oleic acid produced peroxides while poly-unsaturated lipids initially produced peroxides and then fragmented into reactive aldehydes. Incubation with mildly oxidized lipids (most likely lipid peroxides) resulted in increased lipid deposition on Balafilcon A lenses compared to unoxidized lipids, but this was not observed for Senofilcon A lenses. Further oxidation of the lipids (carbon chain breakup) on the other hand resulted in diminished lipid deposition for both contact lens types. CONCLUSIONS: This study provides a method for inducing and controlling lipid oxidation so that the effect of lipid oxidation on contact lens binding can be compared. It could be shown that the degree of lipid oxidation has different effects on the lipid deposition on different contact lens types.
Asunto(s)
Lentes de Contacto Hidrofílicos , Metabolismo de los Lípidos/fisiología , Modelos Teóricos , Cromatografía en Capa Delgada , Humanos , Oxidación-ReducciónRESUMEN
This review critically evaluates a broad range of literature in order to show the relationship between meibum, tear lipids and the tear film lipid layer (TFLL). The relationship of meibum composition to dry eye syndrome is briefly discussed. The review also explores the interactions between aqueous and the TFLL by examining the correlations between meibomian lipids and lipids extracted from whole tears, and by considering protein adsorption to the TFLL from the aqueous. Although it is clear to the authors that a normal tear film resists evaporation, an emerging idea from the literature is that the main purpose of the TFLL is to allow the spread of the tear film and to prevent its collapse onto the ocular surface, rather than to be an evaporative blanket. Current models on the possible structure of the TFLL are also examined.
Asunto(s)
Síndromes de Ojo Seco/metabolismo , Lípidos/análisis , Glándulas Tarsales/química , Lágrimas/química , Humanos , Propiedades de SuperficieRESUMEN
(O-acyl) ω-hydroxy fatty acids (OAHFAs) are a recently found group of polar lipids in meibum. Since these lipids can potentially serve as a surfactant in the tear film lipid layer, the surface properties of a molecule of this lipid class was investigated and compared with a structurally related wax ester and a fatty acid. (O-oleyl) ω-hydroxy palmitic acid was synthesized and used as the model OAHFA. It was spread either alone or mixed with human meibum on an artificial tear buffer in a Langmuir trough, and pressure-area isocycle profiles were recorded at different temperatures and compared with those of palmityl oleate and oleic acid. These measurements were accompanied by fluorescence microscopy of meibum mixed films during pressure-area isocycles. The pressure area curves indicated that pure films of the model OAHFA are as surface active as oleic acid films, cover a much larger surface area than either palmityl oleate or oleic acid and show a distinct biphasic pressure-area isocycle profile. The OAHFAs appeared to remain on the aqueous surface and show only a minor re-arrangement into multi-layered structures during repetitive pressure area isocycles. All these properties can be explained by OAHFAs binding weakly to the aqueous surface via an ester group and strongly via a carboxyl group. By contrast, the pressure area profiles of palmityl oleate films indicate that they form multi-layers and oleic acid presumably forms micelles and desorbs into the subphase. When mixed with meibum, similar features as for pure films were observed. In addition, meibum-OAHFA films appeared very homogeneous; a feature not seen with other mixtures. In conclusion these data support the notion that the tested OAHFA is a very potent surfactant which is important in spreading and stabilising meibomian lipid films.
Asunto(s)
Ácidos Grasos Insaturados/fisiología , Lípidos/química , Glándulas Tarsales/química , Lágrimas/fisiología , Cromatografía en Capa Delgada , Ácidos Grasos Insaturados/química , Humanos , Masculino , Persona de Mediana Edad , Ácido Oléico/química , Ácidos Palmíticos/química , Espectroscopía Infrarroja por Transformada de Fourier , Propiedades de Superficie , Tensoactivos/química , Lágrimas/química , Ceras/análisis , Ceras/metabolismoRESUMEN
PURPOSE: Meibomian lipid films have very complex physical properties that enable them to be compressed and expanded without collapsing. These properties can be attributed to the self assembly of the individual components, mainly wax and cholesteryl esters (WE and CE). Here, the surface pressure properties of WEs and CEs films have been compared to evaluate their contributions to meibomian lipid films. METHODS: Films of different WEs and CEs were spread on a Langmuir trough and their surface pressure area profiles were compared with a particular emphasis on the effects caused by the degree of saturation of the alkyl/alkene chains. RESULTS: Fully saturated WEs and CEs formed unstable films that collapsed upon compression. Very unsaturated waxes and CEs tended to have two distinct phases, one that reflects interaction with the aqueous subphase, while the second appeared to be with the multilayered bulk of the lipid film. With aging of the films, the WEs tended to move off the surface into the bulk. When meibomian lipid films were seeded with large amounts of WEs, only minor changes could be seen unless the WE was very unsaturated. CONCLUSIONS: These data are consistent with meibomian lipid films having a surfactant layer with a complex bulk layer external to this. It is speculated that the bulk layer contains thermotropic smectic chiral liquid crystals of CEs that are interacting with the WEs. This structure would tend to prevent collapse of the meibomian lipids onto the ocular surface and be very tolerant of lipophilic contaminants.
Asunto(s)
Proteínas del Ojo/análisis , Metabolismo de los Lípidos , Lípidos/análisis , Glándulas Tarsales/química , Lágrimas/química , Humanos , Propiedades de SuperficieRESUMEN
CONTEXT: The insulin-like growth factor (IGF) system exerts many effects on the growth and differentiation of both normal and malignant cells. The serum concentrations of insulin-like growth factor I (S-IGF-I), insulin-like growth factor-binding protein 2 (S-IGFBP-2) and insulin-like growth factor-binding protein 3 (S-IGFBP-3) and their inter-relations may differ in certain disease states from those seen in healthy individuals. OBJECTIVE: To estimate age-, gender- and body mass index (BMI)-specific univariate, bivariate and trivariate 95% reference regions for these components in healthy adults and present indices that will facilitate interpretation of patient observations in relation to these reference regions. DESIGN: Blood samples were taken in the morning from 427 healthy, non-fasting German blood donors of both genders (age range, 18-79 years; BMI range, 16-44 kg/m(2)). Reference regions were developed with multivariate regression methods. RESULTS: Regression analyses showed that S-IGF-I and S-IGFBP-3 levels decrease with increasing age, whereas S-IGFBP-2 concentrations increase with age (P<0.0001). Females had significantly higher S-IGFBP-3 levels than males (P<0.0001) and similar S-IGF-I and S-IGFBP-2 concentrations. Increasing BMI was associated with decreasing S-IGFBP-2 (P<0.0001), but was not significantly associated with the concentrations of the other two analytes. Controlling for age, gender and BMI, S-IGF-I and S-IGFBP-3 were positively correlated (r=0.58), whereas S-IGF-I and S-IGFBP-2, and S-IGFBP-2 and S-IGFBP-3 were negatively correlated (r=-0.11 and r=-0.18, respectively). Based on the regression models, which were controlled for age, gender and BMI, two- and three-dimensional 95% reference regions with associated patient indices were described for each pair of analytes and for the trio of analytes, respectively. CONCLUSIONS: The multivariate reference regions developed in this study should be useful in identifying patients with an abnormal IGF-IGFBP axis. It is suggested that introducing multidimensional reference regions and the described patient indices into clinical practice may aid monitoring of the safety of GH therapy. These patient indices may also be useful in the assessment of cancer risk.
Asunto(s)
Envejecimiento/fisiología , Proteína 2 de Unión a Factor de Crecimiento Similar a la Insulina/sangre , Proteína 3 de Unión a Factor de Crecimiento Similar a la Insulina/sangre , Factor I del Crecimiento Similar a la Insulina/metabolismo , Adolescente , Adulto , Anciano , Índice de Masa Corporal , Femenino , Humanos , Masculino , Persona de Mediana Edad , Valores de Referencia , Análisis de Regresión , Factores Sexuales , Adulto JovenRESUMEN
The measurement of insulin-like growth factor-I (IGF-I) has become an essential tool for diagnosing growth hormone deficiency and acromegaly, as well as for monitoring the efficacy of treatment in these disorders. The latter aspect gains significance in the light of epidemiological studies which indicate a relationship between IGF-I levels and the incidence of certain malignancies. We aimed to evaluate the performance of widely implemented IGF-I assays by testing four representative, commercially available immunoassays. Thus, four parallel determinations of the IGF-I levels of 427 healthy blood donors aged between 18 and 79 years were conducted. Apart from divergent performance criteria, the assays also differed systematically. These differences were, however, linear and of lower magnitude among the lower ranges. We conclude that despite the wide variance among commercially available IGF-I assays, which principally involve assay-specific normative data, each of the implemented assays was robust and thus an appropriate tool in the diagnostic work-up of growth hormone deficiency in adult life, when IGF-I levels are low.