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Qi H, Chen Y, Zhu X. [Studies on the change of extracellular matrix in the corneal tissue after photorefractive keratectomy in rabbits]. [ZHONGHUA YAN KE ZA ZHI] CHINESE JOURNAL OF OPHTHALMOLOGY 2001; 37:87-9. [PMID: 11864397] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/23/2023]
Abstract
OBJECTIVE To investigate the relationship between the haze formation and the change of extracellular matrix (ECM) in the corneal tissue after photorefractive keratectomy (PRK). METHODS Twenty-four adult New Zealand White rabbits received PRK in the right eye for minus sign10.00 D ablation. According to the time of rabbits sacrifice, they were divided into 8 groups, and 3 rabbits were in each group. They were immediate, 24 hour, 1 week, 2 week, 1 month, 3 month, 6 month and 12 month groups. After surgery, the corneas were examined periodically by slip-lamp microscopy for haze formation. The right eyes were enucleated, and the corneas were studied with immunohistochemical evaluation for extracellular matrix, including collagen type I, type III, type VI, cellular fibronectin, tenascin and laminin. RESULTS The incidence of haze was 100% after PRK. The formation of haze had a tendency from mild to severe, and along with the time prolongation, it gradually decreased and disappeared. The newly synthesized collagen type I, type III, type VI, cellular fibronectin, tenascin and laminin were deposited in the anterior corneal stroma. CONCLUSION The formation of haze is closely related to the deposition of ECM elements in the anterior corneal stroma in the surgical area.
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Connon CJ, Meek KM, Newton RH, Kenney MC, Alba SA, Karageozian H. Hyaluronidase Treatment, Collagen Fibril Packing, and Normal Transparency in Rabbit Corneas. J Refract Surg 2000; 16:448-55. [PMID: 10939725 DOI: 10.3928/1081-597x-20000701-08] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE Hyaluronidase treatment is the initial step of corneaplasty, a treatment under development that induces stromal softening and involves the application of a custom designed forming lens to achieve modification of refractive error. The purpose of this investigation was to examine changes in the arrangement of stromal collagen fibrils after hyaluronidase treatment. METHODS Rabbit corneas were evaluated by slit-lamp microscopy at 0, 2 and 7 days after treatment and haze was assessed by subjective observation. Molecular and interfibrillar Bragg spacing of corneal collagen were measured from synchrotron x-ray scattering patterns. Transmission electron microscopy and digital image analysis were used to calculate radial distribution functions from the positions of collagen fibrils. The calculated fibril sizes and positions were also used to predict the transmission of visible light through these corneas. RESULTS Hyaluronidase-treated corneas were shown to have a decreased interfibrillar Bragg spacing of 15% to 21%. Fibril hydration did not change. Transparency of these corneas remained unaltered. CONCLUSIONS Hyaluronidase reduced the hydration of the corneal stroma, which led to a more compacted collagen fibril arrangement. This compression was predicted to cause a small reduction in the transmission of visible light through the cornea but not to a point likely to cause visual impairment.
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Ringvold A, Anderssen E, Kjønniksen I. Distribution of ascorbate in the anterior bovine eye. Invest Ophthalmol Vis Sci 2000; 41:20-3. [PMID: 10634595] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/15/2023] Open
Abstract
PURPOSE To analyze the ascorbate distribution in the anterior eye wall to better understand the functional significance of this compound in the eye. METHOD Ascorbic acid was determined by high-performance liquid chromatography using an LC-10 system (Shimadzu, Kyoto, Japan). Bovine eye samples were used. RESULTS The highest ascorbate concentration was observed in the corneal epithelium, with significantly higher values in the central (1.56 mg/g) than in the peripheral (1.39 mg/g) area. The ascorbate content was similar in the corneal stroma (0.22 mg/g), the Descemet's membrane (DM)/endothelium (0.22 mg/g), and the aqueous humor (0.21 mg/ml). By comparison, the sclera (0.15 mg/g) and the conjunctiva (0.11 mg/g) showed lower values, as did the lacrimal gland (0.09 mg/g) and the serum (0.0008 mg/ml). CONCLUSIONS (1) Peak ascorbate concentration was observed in the central corneal epithelium covering the pupillary area. This is compatible with the idea that the ascorbate may act as an UV filter shielding internal eye structures from radiation damage. (2) The ascorbate concentration in the corneal stroma and DM/endothelium was as high as in the aqueous humor, and it is suggested that the aqueous humor plays a key role in the distribution of ascorbate to the anterior eye wall.
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Doughty MJ. Assessment of the effects of cetylpyridium chloride on water content of the collagen-keratocyte matrix of the mammalian corneal stroma ex vivo. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1426:449-58. [PMID: 10076061 DOI: 10.1016/s0304-4165(98)00166-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The effects of cationic surfactants on the time-dependent increases in hydration of the corneal stroma were investigated to assess if the contribution of the proteoglycans could be titrated and how it might relate to the maximum and minimum swelling properties of the corneal stroma. From recent post-mortem eyes from adult sheep, square (8 x 8 mm) samples of corneal stroma were prepared and incubated in isotonic neutral pH mixed salts solution with added glucose, or pure water, at 37 degrees C. The time-dependent changes in wet mass were assessed over 24 h in the absence or presence of 0. 001-2% w/v cetylpyridium chloride (CPC) or benzalkonium chloride (BAC). The rate and magnitude of stromal swelling was reduced in a concentration-dependent fashion by the surfactants. In mixed salts solution, 100% inhibition of swelling could be achieved at 2% CPC and BAC. In pure water, the relative swelling was much more substantial and could only be attenuated by CPC.
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White J, Werkmeister JA, Ramshaw JA, Birk DE. Organization of fibrillar collagen in the human and bovine cornea: collagen types V and III. Connect Tissue Res 1998; 36:165-74. [PMID: 9512886 DOI: 10.3109/03008209709160218] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The localization and fibrillar organization of collagen types V and III in the human and bovine corneal stromas were studied. In the chicken cornea, type V co-assembles with type I collagen as heterotypic fibrils and this interaction is involved in the regulation of fibril diameter necessary for corneal transparency. To determine whether this is a regulatory mechanism common to the corneas of different species the human and bovine corneal stroma were studied. Collagen type V was found in the epithelium and Bowman's membrane in the untreated adult human and bovine cornea using immunofluorescence microscopy. In the absence of any treatment, there was no type V reactivity within the stroma. However, type V collagen was detected homogeneously throughout the corneal stroma after treatments that partially disrupt fibril structure. The reactivity was strongest in the cornea, weaker in the limbus and weakest in the sclera. Fetal corneas showed similar reactivity for type V collagen, but unlike the adult, the stroma was slightly reactive. Immunoelectron microscopy demonstrated that type V collagen was associated with disrupted, but not with intact, fibrils in both human and bovine corneal stroma. Type III collagen reactivity was not detected in the cornea, but was present subepithelially in the limbus and in the scleral stroma. These data indicate that type V collagen is a component of striated collagen fibrils throughout the human and bovine corneal stromas. The interaction of type I and V collagen as heterotypic fibrils masks the helical epitope recognized by the monoclonal antibody against type V collagen. The heterotypic interactions of collagen type V indicate a role in the regulation of fibril diameter analogous to that described in the avian cornea.
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Daxer A, Misof K, Grabner B, Ettl A, Fratzl P. Collagen fibrils in the human corneal stroma: structure and aging. Invest Ophthalmol Vis Sci 1998; 39:644-8. [PMID: 9501878] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
PURPOSE Transparency and biomechanical properties of the cornea depend on the structure and organization of collagen fibrils. The authors determined diameter, axial period, and lateral molecular spacing of collagen fibrils in human corneal stroma as a function of age. METHODS Seventeen normal human corneas were investigated in their native state by means of small-angle and wide-angle x-ray scattering. RESULTS The mean radius of collagen fibrils, the axial period of collagen fibrils, and the lateral intermolecular Bragg spacing were found to be age dependent. The authors determined fibril radii of 16.1 +/- 0.5 nm in persons older than 65 years of age (n = 10) and 15.4 +/- 0.5 nm (mean +/- SD) in persons younger than 65 years (n = 7) (P < 0.022). The related age-dependent values were 66.4 +/- 0.7 nm (> 65 years) and 65.2 +/- 0.8 nm (< 65 years) for the axial period (P < 0.006) and 1.515 +/- 0.010 nm (> 65 years) and 1.499 +/- 0.013 nm (< 65 years) for the intermolecular Bragg spacing (P < 0.022). CONCLUSIONS Aging is related to a three-dimensional growth of collagen fibrils in the human corneal stroma. The age-related growth of the fibril diameter was mostly a result of an increased number of collagen molecules and, in addition, to some expansion of the intermolecular Bragg spacing probably resulting from glycation-induced cross-linking. The observed expansion of the fibrils in an axial direction may result from reduction of the molecular tilting angle within collagen fibrils. The observed alterations of the collagen framework may have implications for refractive surgery and ocular tonometry achieved through related changes in the biomechanical properties of the cornea.
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Langefeld S, Reim M, Redbrake C, Schrage NF. The corneal stroma: an inhomogeneous structure. Graefes Arch Clin Exp Ophthalmol 1997; 235:480-5. [PMID: 9285215 DOI: 10.1007/bf00947003] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
PURPOSE This study was conducted to determine the elemental composition of the human cornea. Special attention was paid to corneal stroma inhomogeneity. METHODS Seventy human corneas were examined by means of energy-dispersive X-ray analysis. Epithelium, subepithelium, middle stroma, sub-Descemet layer, Descemet's membrane and endothelium were subjected to repeated measurements. RESULTS In the cellular layers the phosphorus concentrations were high [0.35 mol/kg dry weight (dw) in the epithelium and 0.403 mol/kg dw in the endothelium]. Similar concentrations were found for sulphur (0.38 mol/kg dw in the epithelium). Stromal layers showed high contents of sulphur: 0.26 mol/kg dw. The phosphorus concentration was found to be higher in the subepithelium than in the middle stroma. Sulphur concentrations were highest in Descemet's membrane, followed by the subepithelium and the middle stroma. DISCUSSION Nucleic acids and energy-containing phosphates explain the high levels of phosphorus in the cellular layers. The high sulphur concentrations may be related to the phosphoadenosinphosphosulfate and protein turnover in the epithelium. We interpret the inhomogeneous distribution of phosphorus in the stroma as a function of the density of keratocytes. An evaluation of all known sulphur-containing biochemical components of the stroma (0.217 mol sulphur/kg dw) corresponds to our measurements. In contrast to former results we find the corneal stroma to be an inhomogeneous structure.
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Feil SH, Barraquer J, Howell DN, Green WR. Extrusion of abnormal endothelium into the posterior corneal stroma in a patient with posterior polymorphous dystrophy. Cornea 1997; 16:439-46. [PMID: 9220242] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
PURPOSE To report the presence of abnormal endothelium that extruded into the posterior corneal stroma in a patient with posterior polymorphous dystrophy. METHODS The corneal button of a man who underwent penetrating keratoplasty for posterior polymorphous dystrophy was examined by light and electron microscopy. Immunoperoxidase staining for cytokeratins, vimentin, and the endothelial antigen recognized by monoclonal antibody 2B4.14.1 antigen was performed. Two-color immunofluorescence staining for simultaneous detection of cytokeratins and 2B4.14.1 antigen was also done. RESULTS Much of the endothelium had characteristic features of epithelium-like cells, and abnormalities in Descemet's membrane were present. Curious oval and slit-like spaces in the posterior stroma were lined by epithelium-like endothelial cells and were continuous with the anterior chamber through defects in Descemet's membrane. CONCLUSION These abnormalities in the posterior stroma have not previously been described in histopathologic reports of posterior polymorphous corneal dystrophy and are likely an unusual variation in the spectrum of this hereditary disorder.
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Smolek MK, Beekhuis WH. Collagen fibril orientation in the human corneal stroma and its implications in keratoconus. Invest Ophthalmol Vis Sci 1997; 38:1289-90. [PMID: 9191590] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
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Rawe IM, Leonard DW, Meek KM, Zabel RW. X-ray diffraction and transmission electron microscopy of Morquio syndrome type A cornea: a structural analysis. Cornea 1997; 16:369-76. [PMID: 9143815] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
PURPOSE This case report describes the structural characterization of the corneal stroma from a patient with Morquio syndrome type A. METHODS A left penetrating keratoplasty was performed, and the cornea was examined using transmission electron microscopy and synchrotron x-ray diffraction. The interfibrillar proteoglycans were visualized in the electron microscope by using cuprolinic blue. RESULTS Stromal collagen fibrils showed a bimodal distribution of diameters: 70% had a distribution comparable to that in normal tissue (20-30 nm) and 30% contained larger fibrils (30-42 nm) as seen by electron microscopy. Both electron microscopy and x-ray diffraction showed that the bulk numeric density of fibrils per unit area in cross-section (number density) was higher than normal in the Morquio syndrome cornea. The arrangement of proteoglycans throughout most of the Morquio syndrome cornea appeared normal, but many of the filaments were twice their normal length. In the anterior stroma, very large proteoglycan filaments (< or = 400 nm long) were found. Other ultrastructural differences also were noted, including abnormal keratocytes and long spacing collagen. CONCLUSION The variation in fibril diameter and number density were modeled to account for only a 5% decrease in light scattering compared with the normal cornea. The extensive corneal clouding seen in the Morquio syndrome cornea cannot therefore be attributed to the variation in fibril diameters; collagen-free areas and expanded cells seem to be the most likely cause.
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Quantock AJ, Klintworth GK, Schanzlin DJ, Lenz ME, Thonar EJ. Proteoglycans contain a 4.6-A repeat in corneas with macular dystrophy: II. Histochemical evidence. Cornea 1997; 16:322-6. [PMID: 9143806] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
PURPOSE Synchrotron x-ray diffraction experiments indicate that corneas with macular corneal dystrophy (MCD) contain unusual 4.6-A periodic repeats thought to reside in proteoglycans or glycosaminoglycans. Recently the 4.6-A x-ray reflection was found to be significantly diminished after incubation of MCD specimens in buffer containing chondroitinase ABC or N-glycanase. We examined the sulfated proteoglycans in these glycosidase-digested MCD corneas. METHODS Transmission electron microscopy was used in conjunction with cuprolinic blue-staining for sulfated proteoglycans. RESULTS Incubation of an MCD specimen in enzyme buffer left both small and large proteoglycan filaments in the stromal matrix, whereas incubation in the presence of chondroitinase ABC removed these molecules from the tissue. Incubation in buffer containing N-glycanase, on the other hand, removed the large proteoglycan filaments from the MCD stroma but left unaffected the small collagen-associated proteoglycans. CONCLUSION These results are consistent with the interpretation that 4.6-A periodic repeats in MCD corneas reside in large sulfated proteoglycan filaments (or aggregates thereof) that may contain chondroitin/dermatan sulfate and keratan sulfate or keratan components.
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Møller-Pedersen T. A comparative study of human corneal keratocyte and endothelial cell density during aging. Cornea 1997; 16:333-8. [PMID: 9143808] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
PURPOSE To investigate whether the human corneal keratocyte density changes during aging. METHODS Comparative data on keratocyte and endothelial cell density (ECD) were obtained from 178 normal corneas (89 persons ranging in age from 30 weeks of gestation to 90 years). Keratocyte density was quantified by using biochemical measurements of the stromal DNA/ mass content within the central 7-mm diameter zone (sDNA) (1 U equals 1 microgram DNA per milligram of dry tissue weight), whereas central ECD was assessed after alizarin red staining. RESULTS In the first decade of life, there was a mean sDNA of 1.64 +/- 0.29 U, corresponding to 6.22 +/- 1.1 x 10(4) keratocytes per mm3. A direct correlation between keratocyte density and donor age was found (r = -0.49; p < 0.0001) with a physiologic decline of 0.3% per year throughout life (density = 6.30 x 10(4) keratocytes per mm3-190 x age). A similar decrease of 0.3% per year was observed in the ECD during adulthood, whereas the annual decline was 2.9% during infancy and childhood. The interindividual variation in keratocyte density was of the same magnitude as that seen in ECD. Moreover, keratocyte density was positively correlated with ECD (r = 0.23; p < 0.001); however, after correcting for age by multiple regression analysis, this correlation disappeared, indicating that keratocytes and endothelial cells form distinct cell populations. CONCLUSIONS The study demonstrates a linear loss of human corneal keratocytes as a function of age, a loss that parallels the well established decline in ECD.
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Abstract
PURPOSE To investigate the organization of collagen fibrils in the lyophilized cornea. METHODS Freshly harvested porcine corneas (n = 10) were lyophilized and examined by synchrotron x-ray diffraction and transmission electron microscopy. RESULTS Collagen fibrils are highly compacted in lyophilized corneas. They become more widely spaced when the tissue is rehydrated, however, the distribution of imbibed water throughout the stroma is not necessarily homogeneous within an individual cornea, nor is it always similar in specimens that have been rehydrated to similar levels. In lyophilized corneas, the mean center-to-center interfibrilar spacing of the regularly arranged collagen reaches levels found in freshly thawed porcine corneas (between 74% and 78% water by weight) when between 74.3% and 81.6% of the rehydrated lyophilized cornea's weight is water. CONCLUSION Regularly arranged collagen fibrils are able to reapproximate their original spacings if lyophilized corneal tissue is rehydrated, although the manner in which imbibed water is distributed is somewhat unpredictable.
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Daxer A, Fratzl P. Collagen fibril orientation in the human corneal stroma and its implication in keratoconus. Invest Ophthalmol Vis Sci 1997; 38:121-9. [PMID: 9008637] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
PURPOSE The kind and the degree of preferred collagen fibril orientation in normal human corneal stroma were investigated as important qualities of the cornea with respect to its mechanical properties and, hence, to refractive surgery. To determine whether this information is relevant to corneal disease, the authors investigated collagen fibril orientation in several corneas with keratoconus. METHODS By means of low-angle x-ray scattering, 17 normal human corneas and four corneas of eyes with keratoconus were investigated. RESULTS Collagen fibrils in the normal human corneal stroma showed two preferred orientations orthogonal to each other. These were the horizontal and the vertical directions. The authors defined a degree of orientation gamma, determined to be gamma = 0.49 +/- 0.10 (mean +/- SD). This means that the excess of the preferentially oriented fibrils in relation to the total number of fibrils was approximately 49%. It follows from this value that approximately two thirds of the fibrils (66%) were within in a 45 degrees sector (+/-22.5 degrees) around the horizontal and vertical meridians, whereas approximately one third (34%) is oriented in the oblique sectors in between. No statistically significant variation of gamma within a central 7 mm zone could be detected in normal corneas. The orthogonal arrangement of the collagen fibrils was, however, profoundly altered in keratoconus, in which nonorthogonal orientations were found inside the apical scar. CONCLUSIONS The normal human corneal stroma shows a considerable degree of structural anisotropy. It is characterized by two preferred collagen fibril orientations orthogonal to each other. Alteration of the regular orthogonal arrangement of the fibrils in keratoconus may be related to the biomechanical instability of the tissue.
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Tong H, Zhang L, Dai S, Bai C. [Lectin-binding histochemical study on developing corneal epithelium and stroma of normal human being]. YAN KE XUE BAO = EYE SCIENCE 1996; 12:178-82. [PMID: 15508249] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/01/2023]
Abstract
PURPOSE To study glycoconjugates in developing cornea of normal human. METHODS Lectin-binding histochemical method with five biotin-coupled lectins (conA, LCA, PNA, WGA, RCA). RESULTS 1. WGA mainly stained the membrane of epithelial cells, especially in surface cells. It also stained anterior stroma of embryo. 2. All the layers of epithelium could be stained by conA, uneven stain was seen in stroma of embryo corneas. 3. RCA, LCA receptor distributed in base of cornea epithelium. 4. PNA can only stain cornea epithelium of 16 embryo. CONCLUSIONS 1. Glycoconjugates of binding conA, WGA, PNA, LCA, RCA are in the developing corneas of human. 2. The distribution of these lectin receptors may change with corneal developing. It may be related to the maturity of corneas.
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Peters DM, Kintner RL, Steger C, Bultmann K, Brandt CR. Maturation of collagen fibrils in the corneal stroma results in masking of tyrosine-rich region of type V procollagen. Invest Ophthalmol Vis Sci 1996; 37:2047-59. [PMID: 8814144] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
PURPOSE To determine the molecular form of type V procollagen in collagen fibrils in mammalian corneal stromas. METHODS The presence of the tyrosine-rich region in the NH2-propeptide of type V procollagen in collagen fibrils was examined in human, bovine, and mouse corneas and human corneal fibroblast cultures by immunofluorescence microscopy and immunoblot analysis using a polyclonal antibody specific for this region. The antibody was generated using a glutathione S-transferase-fusion peptide. RESULTS The tyrosine-rich region was detected readily in frozen sections of 5- to 6-month-old mouse corneal stromas without the need for any unmasking techniques, indicating that this domain is exposed on the surface of striated collagen fibrils. In contrast, frozen sections of adult human and bovine corneas did not label with the polyclonal sera to the tyrosine-rich region. Immunoblot analysis of bacterial collagenase digests of human and bovine corneas, however, indicated that peptide fragments containing the tyrosine-rich region of type V procollagen and of the expected molecular weight of 70 to 85 kDa were present. Further immunofluorescence microscopic studies and immunoblot analysis of mouse corneas at different ages and of collagen fibrils formed in human corneal fibroblast cultures over time indicated that, initially, the tyrosine-rich region of type V procollagen could be detected in all these collagen fibrils; however, as the age of the mouse and the culture increased, the ability to detect this region decreased. CONCLUSIONS These results suggest that, in vivo, the tyrosine-rich region of type V procollagen is retained on type V procollagen molecules within mammalian collagen fibrils from corneal stromas and that this region becomes masked as collagen fibrils mature or the species ages.
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Liu SH, Gottsch JD. Amino acid sequence of an immunogenic corneal stromal protein. Invest Ophthalmol Vis Sci 1996; 37:944-8. [PMID: 8603881] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
PURPOSE A unique cornea-associated antigen (CO-Ag) has been purified previously from stromal extracts. The protein is the target for autoantibodies in patients with Mooren's ulcer. In this study, the amino acid sequence of CO-Ag was analyzed and the structure-function properties of CO-Ag was determined. METHODS Purified CO-Ag was subjected to N-terminal sequencing by automated Edman degradation. Binding of calcium (Ca2+) to CO-Ag was measured by a direct (45)Ca2+ -binding assay. RESULTS The complete amino acid sequence of CO-Ag has been determined. The protein contains 70 amino acids in a single chain and lacks cysteine, tryptophan, and methionine residues. A computerized data base search of protein and nucleic acid sequences revealed strong homology to the Ca2+ -binding proteins of the S-100 family. The sequence of CO-Ag shows a high homology with calgranulin C (CaG-C) previously purified from pig granulocytes. The functional Ca2+ -binding sites of CO-Ag and CaG-C were different based on homology with known Ca2+ -binding domains and their Ca2+ -binding properties. There are three amino acid substitutions in the N-terminal Ca2+ -binding domain. Differences were functionally conserved and compatible, with minimum single-base changes in the codon structures. The greatest difference was located in the C-terminal Ca2+ -binding domain. Five consecutive amino acid changes from D63-K-K-G-A67 in CO-Ag to M63-Q-D-E-Q67 occurred in CaG-C. These differences alter the structure of CO-Ag, which no longer can bind Ca2+ ions. The existence of this nonfunctional Ca2+ -binding site was corroborated by its Ca2+ -binding properties. The number of Ca2+ -binding sites for the CO-Ag sub-unit is approximately half that of the CaG-C monomer, although these two proteins have a similar low binding constant of approximately 2 x 10(-4) M. CONCLUSIONS These results suggest that CO-Ag is a new member of the Ca2+ -binding protein of the S-100 family heretofore undescribed in the cornea. Sequence data provide an important framework to search for sequence similarity with microbial proteins as possible substrates for molecular mimicry and for the identification of possible pathogenic epitopes in CO-Ag.
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Habib MS, Speaker MG, Schnatter WF. Mass spectrometry analysis of the by-products of intrastromal photorefractive keratectomy. OPHTHALMIC SURGERY AND LASERS 1995; 26:481-3. [PMID: 8963863] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
BACKGROUND AND OBJECTIVE To determine the nature and chemical composition of the cavitation bubbles generated by intrastromal photorefractive keratectomy (IPRK) with the Neodymium: Yttrium Lithium Fluoride (Nd:YLF) picosecond laser. MATERIALS AND METHODS IPRK was performed on the corneas of three fresh human cadaver eyes with the Nd:YLF picosecond laser. High energy levels of 200 mJ/pulse to 300 mJ/pulse were used to produce the maximum amount of gas within the corneal stroma. The cavitation bubbles produced in the stroma were aspirated using a gas-tight syringe connected to a valve, and the specimens were analyzed with a mass spectrometer. RESULTS The experiment was performed on three different occasions using one cadaver eye in each experiment. The analysis consistently revealed a mixture of carbon dioxide, carbon monoxide, water vapor, oxygen, and nitrogen. Atmospheric control samples also revealed oxygen and nitrogen. No other components were detected. CONCLUSION The gaseous by-products of IPRK with the picosecond laser result from the simple breakdown of stromal tissue and contain no toxic or unexpected components. We found that these gaseous products are capable of rapid elimination by absorption or diffusion out of the intact cornea.
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Gottsch JD, Liu SH, Minkovitz JB, Goodman DF, Srinivasan M, Stark WJ. Autoimmunity to a cornea-associated stromal antigen in patients with Mooren's ulcer. Invest Ophthalmol Vis Sci 1995; 36:1541-7. [PMID: 7601634] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
PURPOSE To purify and characterize a cornea-associated antigen (CO-Ag) and to determine antibody levels to CO-Ag in patients with Mooren's ulcer. METHOD Standard ion exchange and gel filtration chromatographies were used to isolate and purify CO-Ag from crude bovine stromal extracts. The serum of a patient with Mooren's ulcer, containing a high level of antibodies directed against CO-Ag, was used to monitor isolation procedures. Using this newly purified CO-Ag, an enzyme-linked immunoabsorbent assay was used to detect the presence of antibodies to CO-Ag in the sera of other patients with Mooren's ulcer. RESULTS CO-Ag was purified to apparent homogeneity from bovine corneal stromal extracts by a series of ion exchange chromatographies and gel filtration. Polyacrylamide gel electrophoresis showed that CO-Ag was a tetramer with a molecular weight of 30,000 d that may dissociate under denaturing conditions into a monomer of 7000 d. Strong indirect immunofluorescent staining was demonstrated of the stroma by guinea pig anti-CO-Ag antibody. A statistically significant difference in the level of specific antibodies to CO-Ag between patients with Mooren's ulcer and controls was found (P < 0.001). The antibody level was elevated in patients with Mooren's ulcer (mean antibody level, 0.58 +/- 0.13) compared with the controls (mean antibody level, 0.22 +/- 0.04). CONCLUSION These results suggest that an autoantigen exists in the corneal stroma that reacts with serum antibodies from patients with Mooren's ulcer. The availability of a purified corneal antigen could facilitate the diagnosis and define the pathogenetic mechanisms in Mooren's ulcer.
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Delaigue O, Arbeille B, Rossazza C, Lemesle M, Roingeard P. Quantitative analysis of immunogold labellings of collagen types I, III, IV and VI in healthy and pathological human corneas. Graefes Arch Clin Exp Ophthalmol 1995; 233:331-8. [PMID: 7672619 DOI: 10.1007/bf00200481] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
BACKGROUND We studied the distribution of collagen types I, III, IV and VI in one healthy human cornea and in seven pathological human corneas, in which the disorders were three cases of pseudophakic bullous keratopathy (two severe, one moderate) and one case each of stage IV keratoconus, chronic ulcer, vascularized cornea and disciform keratitis. METHODS Transmission electron microscopy examinations were performed on post-embedding immunogold-labelled sections. The staining was evaluated by gold particle count in the different tissues. The presence or absence of a given antigen was determined by statistical analysis, using a d-value test. RESULTS Our results on healthy corneal tissues corroborate the data available from previous studies, except for collagen type VI, which we found to be absent in Bowman's layer. In pathological corneas with a collagenous layer posterior to Descemet's membrane, collagen types I, III and especially IV were detected in this collagenous layer. Collagen types I, III and VI were detected in the anterior healed stroma of other pathological corneas, except for the keratoconus cornea, in which intense collagen III staining was observed. CONCLUSION The presence of collagen types I and III in the posterior collagenous layer of our pseudophakic bullous keratopathy corneas suggests that this layer corresponds to scar tissue secreted by stimulated endothelial cells.
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Twining SS, Fukuchi T, Yue BY, Wilson PM, Zhou X. Alpha 1-antichymotrypsin is present in and synthesized by the cornea. Curr Eye Res 1994; 13:433-9. [PMID: 7924407 DOI: 10.3109/02713689408999871] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The proteinase inhibitor alpha 1-antichymotrypsin is present in the epithelial, stromal and endothelial layers of the human cornea. This was determined by immunolocalization in corneal sections and by Western blot analysis of extracts from the three separated layers. The inhibitor was quantified in the extracts by immunodot blot analysis. The levels observed were 1.3 +/- 0.3 microgram/cornea for the epithelial layer, 22.8 +/- 3.8 micrograms/cornea for the stromal layer and an average of 0.17 micrograms/cornea for the endothelial layer. alpha 1-Antichymotrypsin is being synthesized by the cornea. Metabolically labeled inhibitor was immunoprecipitated from the three layers following organ culture of the intact cornea. Two major forms were detected. These were the native, mature 64 kDa form and a 50 kDa form which is either a degradation product or an incompletely glycosylated form. These results indicate that the cornea has the ability to locally control degradation through synthesis of this inhibitor. Local synthesis of this inhibitor releases the cornea from total dependance upon the vascular system for its supply of alpha 1-antichymotrypsin.
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Quantock AJ, Kratz-Owens KL, Leonard DW, Meek KM, Schanzlin DJ. Remodelling of the corneal stroma after lamellar keratoplasty. A synchrotron x-ray diffraction study. Cornea 1994; 13:20-7. [PMID: 8131402 DOI: 10.1097/00003226-199401000-00005] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Patients healing from lamellar keratorefractive surgeries invariably experience postoperative corneal haze. In our lamellar keratoplasty (LKP) rabbit model, visual recovery is concomitant with the invasion of the grafted tissue by viable keratocytes from adjacent host tissue, and the return of corneal clarity is attributed to the remodelling of the stromal tissue by these keratocytes. We used synchrotron x-ray diffraction techniques to elucidate the ultrastructure of the stromal collagen fibrils in rabbit corneas at various time points in the 3 months after LKP surgery. Lenticules were frozen in 50% of the cases. The average spacing of the collagen molecules, which constitute the stromal fibrils, remains unchanged by LKP in both frozen (1.69-1.73 nm) and nonfrozen (1.58-1.75 nm) cases. In the nonfrozen case, the collagen fibril diameters are initially slightly larger than normal (38.3-41.9 nm) but have receded by 2 months postoperatively [similar to the frozen cases (37.7-41.9 nm)]. The post-LKP spacing of the collagen fibrils in the nonfrozen corneas is unremarkable (56.2-69.2 nm). In contrast, the increased collagen interfibrillar spacing in the frozen case is considerable (56.7 to > 94.6 nm) and variable up to 21 days postoperatively. Because the changes in interfibrillar spacing did not always mirror pachymetry changes in the frozen cases, we suspect occasional graft malapposition or the formation of intrastromal, fluid-filled, collagen-free "lakes."
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Abstract
The ultrastructural distribution of hyaluronan (hyaluronic acid) in rat cornea was investigated using tissue processed by osmium tetroxide/microwave fixation and epoxy resin embedding or by glutaraldehyde/microwave fixation and lowicryl K4M embedding. Hyaluronan-binding proteins (HABP) and link proteins (LP) coupled to 15-20 nm gold particles were used as novel ultrastructural markers in a one-step post-embedding procedure. These probes labelled the intra- and extracellular aspects of corneal epithelial and endothelial plasma membranes, as well as those of stromal keratocytes. In the corneal epithelium, wing and superficial cell plasma membranes were intensely stained, whereas basal cells exhibited a weak reaction on their stromal-facing surfaces and an intermediate one on their lateroapical aspects. In the corneal endothelium labelling was associated primarily with the apical and lateral plasma membranes. The labelling intensity associated with keratocyte plasma membranes was weak.
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Fitzsimmons TD, Fagerholm P, Härfstrand A, Schenholm M. Hyaluronic acid in the rabbit cornea after excimer laser superficial keratectomy. Invest Ophthalmol Vis Sci 1992; 33:3011-6. [PMID: 1399404] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Hyaluronic acid (HA) is not normally found in the corneal stroma. Rabbit corneas were examined for the presence of stromal HA after excimer laser treatment. One eye in each of 28 rabbits received a 60 microns deep superficial keratectomy with the excimer laser. After 1, 8, 21, and 60 days, the corneas were analyzed by quantitative and histochemical methods specific for HA. A statistically significant increase in the HA concentration compared to the baseline amount in the untreated fellow eye was seen at 8, 21, and 60 days. HA was visualized histochemically in the anterior stroma of the excimer-treated eyes at all times tested. The presence of HA after excimer surgery may influence the hydration, thickness, and transparency of the cornea. The reactive production of HA in the stroma may represent a nonspecific corneal tissue response to injury.
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Fullwood NJ, Tuft SJ, Malik NS, Meek KM, Ridgway AE, Harrison RJ. Synchrotron x-ray diffraction studies of keratoconus corneal stroma. Invest Ophthalmol Vis Sci 1992; 33:1734-41. [PMID: 1559773] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The aim of this study was to determine any differences in the collagen molecular and fibrillar packing, or the arrangement of the proteoglycans along the fibril axis, in the stroma of keratoconus and control corneas. High and low-angle x-ray diffraction patterns from the fibrillar and molecular packing of collagen in keratoconus and control corneas were obtained using a synchrotron radiation source. The results indicate no difference in interfibrillar spacing between keratoconus and control corneas at normal physiological hydration, or over a range of hydrations (H = 1-11). This unambiguously demonstrates that the thinning of the stroma that occurs in keratoconus is not a result of closer packing of the collagen fibrils in the stroma. Intermolecular spacings were shown to be significantly (P less than 0.001) lower in keratoconus corneas at normal physiological hydration and over a range of hydrations (H = 1-11). Meridional patterns from the axial distribution of electron density along the collagen fibrils were obtained from untreated control and keratoconus corneas and from the corneas after their proteoglycans were stained with cupromeronic blue. Analysis of the integrated intensities of the first nine orders of these reflections show there is a difference in the staining behavior of collagen-associated proteoglycans in control and keratoconus corneas. Determination of the electron density vectors along the collagen fibrils of cupromeronic blue-stained corneas by the use of Patterson functions indicates that the keratoconus corneal stroma has a specific, ordered proteoglycan that is present in lower numbers along the collagen fibrils, and that it stains less with cupromeronic blue or is in a more disordered arrangement than in the controls.
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