The coating of bovine and rabbit corneas denuded of their endothelium with bovine corneal endothelial cells.

A method for coating corneas denuded of their endothelium has been developed. The attachment and spreading of cultured bovine corneal endothelial cells seeded upon the Descemet's membrane of corneal buttons previously denuded of their endothelium by delicately sweeping the endothelial side with a cotton swab have been analyzed. Confluent cultures of bovine corneal endothelial cells were exposed to trypsin to disrupt the cell monolayer into single cells. Increasing concentrations of endothelial cells ranging from 2·5 × 10⁴ to 3 × 10⁵ cells were then seeded on the denuded Descemet's membrane of 11 mm bovine corneal buttons. When the corneal buttons were stained with alizarin red after an incubation period of 8 hr at 37°C, the best coating was observed with 10⁵ seeded cells. In this case, no areas of denudation could be seen and the cells were clearly apposed to one another, thereby reconstituting an endothelial cell monolayer. The cultured bovine corneal endothelial cells seeded on denuded Descemet's membranes plated extremely rapidly. By 15 min, 80% of Descemet's membrane was covered with a monolayer of endothelial cells and by 30 min all of Descemet's membrane was covered.The plating of bovine corneal endothelial cells on denuded Descemet's membrane was a direct function of the trypsin concentration to which they were first exposed. Cells first treated with 0·05% trypsin plated poorly 1 hr after being seeded on a denuded Descemet's membrane. Better plating efficiency was achieved with cells first exposed respectively to 0·025% and 0·01% trypsin. The best results were consistently obtained with cells first dissociated with 0·005% trypsin.Although serum is required in vitro for the attachment of normal cells to tissue culture dishes, it was not required for the attachment of corneal endothelial cells to the denuded Descemet's membrane. Cultured corneal endothelial cells plated equally well in the presence or absence of serum. Similar results were obtained when the cells were suspended in aqueous humor instead of in tissue culture medium.When denuded rabbit corneas were used as a substrate instead of bovine corneas, all the parameters studied for the attachment and spreading of bovine corneal endothelial cells seeded on bovine corneas (cell density, time, and medium) lead to similar conclusions with respect to the interactions between corneal endothelial cells and rabbit Descemet's membrane.     

Regeneration with proliferation of the endothelium of cultured human donor corneas with extended postmortem time

PURPOSE: To examine the endothelium of donor corneas with extended postmortem time for survival and reparative mechanisms in an eye bank organ culture storage system. METHODS: We obtained 14 pairs of donor corneas with a postmortem time ranging from 29 to 163 hours. One cornea of a pair was immediately fixed for the study of structural changes postmortem and to serve as a control. The second was stored in organ culture for 3 days and thereafter fixed to be studied for reparative processes. Examination was done with light microscopy and scanning electron microscopy. Immunohistochemical staining with antibodies against proliferating cell nuclear antigen, Ki-67, and n-cadherin was performed to examine for cell proliferation and to characterize the cells. RESULTS: The control corneas showed increasing endothelial cell damage with increasing postmortem time. After 5-7 days postmortem, most cells were structurally damaged. After 3 days in organ culture, all corneas acquired an endothelial covering of the posterior surface, with cells, suggesting proliferation in both scanning preparations and in cross-sections. Positive endothelial cell staining with proliferating cell nuclear antigen was found in all cultured corneas. Ki-67 staining of the endothelium was found in 9 of the cultured corneas. CONCLUSIONS: The study showed survival of the corneal endothelium up to 7 days postmortem, and accordingly, the potential clinical use of donor corneas with extended postmortem time. Our results furthermore suggest that repair of the endothelium in donor corneas during organ culture storage occurs also by proliferation and not only by migration and enlargement of existing cells. If we uncover the mechanisms regulating cell proliferation in corneal endothelium, it should be possible to develop better storage methods of corneal transplants to improve quality and supply.     

The healing of human corneal endothelium. An in vitro study

A 4 mm circular defect was made on the endothelium by transcorneal freezing of 5 normal human corneas. The eyes were enucleated because of malignant tumours, patient age 3 to 74 years. After excision, the corneas were kept in culture medium for 3 (4) days, and subsequently prepared for SEM. At this stage, the defect was covered with endothelium, whose origin was a narrow zone adjoining the edge of the defect. The endothelium on the peripheral, undamaged part of the cornea did not seem to take part in the repair process, neither by proliferation, enlargement nor by migration. Dividing cells were found scattered on the damaged area. The repair process was found to be similar in all five eyes, irrespective of the age of the patient. In organ culture, the healing of corneal endothelial defects is similar in rabbits and in humans.     

人表皮生长因子对体外培养兔角膜内皮细胞影响的实验研究

目的：明确人表皮生长因子（ｈｕｍａｎ Ｅｐｉｄｅｒｍａｌ Ｇｒｏｗｔｈ Ｆａｃｔｏｒ,ｈＥＧＦ）对角膜内皮细胞的影响。方法：采用体外培养的兔角膜内皮细胞,观察接种后不同时点ｈＥＧＦ对其生长状态的影响;兔角膜片内皮损伤模型,离体培养后行Ｈ－Ｅ染色和Ｈ＾３－ＴｄＲ掺入放射自显影,观察ｈＥＧＦ对其修复的影响。结果：兔角膜内皮细胞体外培养ｈＥＧＦ组细胞数高于对照组,并使细胞形态产生纺锤形改变;角膜内皮细胞     

Transplantation of adult human or porcine corneal endothelial cells onto human recipients in vitro. Part I: Cell culturing and transplantation procedure

PURPOSE: To develop a method for grafting endothelial cells isolated from organ-cultured adult human corneas onto the denuded Descemet's membrane of human recipients. METHODS: Adult human or porcine corneal endothelial cells were isolated and maintained in monolayer cultures before seeding. Recipient corneas were stripped of their own endothelium by one of three different methods (mechanical, chemical, or physical) and the completeness of removal assessed after vital staining. The utility of each method was evaluated by monitoring the quality of attachment of the seeded-cell population. The seeding density of transplanted cells required for optimal results also was determined and the final numeric cell density achieved on recipient corneas after culturing for 7-20 days ascertained. The influence of incubating source cells with fibroblast growth factor (FGF), both on this latter parameter and on cell morphology, also was evaluated. The functional integrity of regrafted endothelium was assessed in 24-h perfusion experiments. RESULTS: The seeding of between 150,000 and 700,000 cells onto recipient corneas, followed by gentle centrifugation to improve attachment, yielded maximal final numeric cell densities of 3,450/mm2 and 1,850/mm2 in porcine and human lines, respectively. Recipient corneas were most effectively denuded of their own endothelium by freezing-and-thawing. The newly established endothelial monolayer remained stable for up to 20 days in organ culture (longest period monitored). FGF treatment did not enhance the final numeric density of cells attained on recipient corneas, but it did have a beneficial effect on their morphology. Only those recipient corneas that exhibited a well-differentiated monolayer of seeded endothelial cells underwent stromal deswelling near to physiologic levels. CONCLUSION: A practical working model has been developed, whereby recipient corneas stripped of their own endothelium can be furnished with a "new," near-normal endothelium by appropriate manipulations of the seeded-cell population. This now paves the way for a realistic tackling of the problem of endothelial cell paucity in donor corneas destined for transplantation.     

Apoptosis in the endothelium of human corneas for transplantation

PURPOSE: To determine whether endothelial cell loss of human corneas stored in organ culture before transplantation is due to apoptosis. METHODS: The corneal endothelium of human corneas, stored in organ culture at 34 degrees C for varying periods of time, were analyzed for the presence of apoptotic cells using the TdT-mediated dUTP nick-end labeling (TUNEL) technique. Corneal endothelial cell apoptosis was confirmed by Hoechst staining and immunolabeling with anti-caspase 3 active antibody. RESULTS: Apoptotic cells were identified in the corneal endothelium of human organ cultured corneas: their number and distribution demonstrated a close correlation with corneal folding and overall quality of the corneal endothelium. TUNEL-positive labeling of cells was confirmed as apoptotic by the presence of morphologic nuclear alterations identified by Hoechst staining and the presence of immunostaining for caspase-3 activity. Corneal endothelial cell apoptosis was independent of cause of donor death, death to enucleation time, and death to culture times. CONCLUSIONS: Corneal endothelial cell apoptosis appears to determine the suitability of a cornea for transplantation.     

Biology in vitro of corneal epithelium and endothelium

Four main areas were explored: 1) the proper medium for culturing corneal tissue; 2) the effect of serum on tissue growth in vitro; 3) the interrelationships in vitro between corneal epithelium and endothelium; and 4) the biology of cultures of whole corneas (organ cultures). Modified Eagle's minimal essential medium (MEM) proved to be an excellent culture fluid. Corneal tissue could be grown in MEM without serum or clot, thus providing a defined culture medium. The biology in vitro of outgrowths of multilayered corneal epithelium and monolayered corneal endothelium are discussed. Contact inhibition between epithelium and endothelium is demonstrated in whole corneal (organ) cultures.From the Laboratory of Ophthalmic Pathology, Scheie Eye Institute, and the Departments of Ophthalmology and Pathology, University of Pennsylvania Medical School.This study was supported by the National Institutes of Health, Training Grant T01-EV-0070-03 from the National Eye Institute.Candidate's thesis for membership in the American Ophthalmological Society, Accepted by the Committee on Thesis May 1975.     

生长因子与角膜内皮细胞

角膜内皮细胞是维持角膜透明的关键细胞成分,角膜内皮细胞密度降低和形态异常可导致内皮细胞功能失代偿而降低视力。在伤口愈合过程中,生长因子可增加角膜内皮细胞密度槿刺激内皮细胞再生,促进伤口愈合。肽类生长因子影响着多种细胞生理过程,包括细胞增殖,分化,移行和存活。     

Synthesis of sulfated mucopolysaccharides by chick corneal fibroblasts in vitro

Whole corneas and the three corneal cell-types (epithelium, endothelium, and fibroblasts) were incubated in vitro for varying lengths of time and then labeled with [³⁵S]sulfate. Freshly isolated whole corneas, corneal stromas, and isolated corneal fibroblasts all incorporated [³⁵S]sulfate into keratan sulfate-like polysaccharide. Neither the corneal epithelium nor the endothelium incorporated label into this polysaccharide. After 48 hr in vitro under a variety of culture conditions, no tissue or isolated cell population continued to synthesize keratan sulfate-like polysaccharide. The cultured corneal tissues continued to synthesize and secrete chondroitin 4-sulfate as well as heparan sulfate, chondroitin 6-sulfate, and a dermatan sulfate-like material. The latter three polysaccharides are not thought to be normal components of the cornea.     

Effects of fibroblast growth factor and chondroitin sulfate on predamaged corneal endothelium. An organ culture study

Fibroblast growth factor (FGF) and chondroitin sulfate (CDS) were used as supplements in organ culture medium to compare the regeneration ability of corneal endothelium with scattered damages. After 1 week of culturing, cell densities in both FGF-supplemented and FGF + CDS-supplemented groups were not higher than the densities of the control groups. Cells in both groups showed polymorphism. In both CDS-supplemented groups, the corneas were thinner. The cell density in the group supplemented with only CDS was higher than that of the control group, but in the CDS + FGF-supplemented group the cell density was not higher than that of the control and the morphology was even worse. Combining of FGF and CDS in culture medium appeared to be disadvantageous.     

兔角膜器官培养保存与应用的研究

目的探讨建立角膜器官培养保存的方法、保存后角膜的特性及其用于移植的可行性。方法选用特定的胎牛血清保存液,密闭保存36只成年新西兰兔角膜于32％恒温箱中;在保存后1～4周的不同时间点,将角膜从保存液取出转入高渗透压的脱水液中脱水48h备用;而后对比保存前后角膜内皮细胞密度、角膜厚度变化,并观测角膜内皮组织学特性和保存中污染情况;器官培养保存后的兔角膜做同种异体穿透性角膜移植,观测术后1周内植片情况;使用荧光标记的抗MHC-Ⅱ分子抗体标示保存后的角膜中树突状细胞,观测其分布和保存后变化特点。结果成功建立了角膜器官培养保存方法,保存中角膜的污染率约8．3％;保存4周内的兔角膜脱水后均透明;保存第3周时,角膜后弹力层周边区有细小皱褶;保存第4周时,全角膜有明显皱褶;器官培养保存的兔角膜内皮细胞密度随保存时间延长而下降,保存4周后兔角膜内皮细胞密度平均下降15．7％;兔角膜厚度随保存时间延长而增加,保存第4周时,角膜中央厚度可达0．7mm;组织学观察可见角膜内皮细胞与后弹力层贴附紧密;树突状细胞分布于角巩膜缘上皮层,保存至第3周时全部消失;同种异体角膜移植术后7d内植片透明,无原发失败。结论本研究建立的角膜器官培养保存方法可使保存的角膜在一定时间内维持活性,角膜的免疫原性下降。     

Transplantation of cultured adult human or porcine corneal endothelial cells onto human recipients in vitro. Part II: Evaluation in the scanning electron microscope

PURPOSE: To evaluate the morphology of endothelial monolayers, which have been regrafted onto the denuded Descemet's membrane, with scanning electron microscopy (SEM). METHODS: Material derived from each of the experimental groups described in part I of this investigation was evaluated in the current study. Recipient corneas, denuded of their native endothelium by mechanical, chemical, or physical debridement, were examined to assess the effectiveness of each technique in killing and removing cells. Porcine or human donor corneal endothelial cells maintained in monolayer culture for up to 10 passages then were seeded onto the denuded Descemet's membranes of recipients in the absence or presence of fibroblast growth factor (FGF). The monolayers thereby established were examined in the SEM, and the morphologic status of individual cells compared with that manifested in normal human donor corneas maintained for 4 weeks in organ culture (reference control). Isolated and cultured human keratocytes regrafted onto the denuded Descemet's membranes of recipient corneas served as nonendothelial control specimens. Tissue was processed for examination in the SEM according to standard techniques. RESULTS: Each of the three methods used to strip recipient corneas of their native endothelium was effective and elicited no gross structural damage to Descemet's membrane. Some small focal defects within this latter layer were, however, observed, these being encountered at higher frequency after mechanical debridement than after chemical or physical stripping. Porcine or human endothelial cells seeded onto the denuded Descemet's membranes of recipient corneas formed stable monolayers. The morphologic status of regrafted cells corresponded to that manifested in monolayer cultures before seeding, porcine ones always being more differentiated than their human counterparts. Poorly differentiated human endothelial cells had a slender, elongated, fibroblast-like appearance, whereas more highly differentiated ones manifested broad, flat, polygonal profiles. Monolayers covered the entire corneal surface and impinged to a variable degree onto the trabecular meshwork, at which juncture cells always assumed a less well-differentiated morphology. FGF consistently effected an increase in differentiation status, and as this became augmented, the capacity of monolayers to violate the corneal-trabecular meshwork border was correspondingly repressed. Seeded keratocytes formed dense, multilayered sheaths, resembling retrocorneal membranes, across the entire corneal surface, trabecular meshwork, and iris root. The surface characteristics of the constituent cells were quite distinct from those manifested by endothelial cells, even the least well-differentiated ones. CONCLUSION: Regrafting of human corneal endothelial cells onto the denuded Descemet's membranes of recipients resulted in the formation of stable monolayers. Because the morphologic status of seeded cells closely mimicked that manifested in monolayer cultures before transplantation, it may be anticipated that efforts to refine and optimize culturing conditions would yield improvements in this parameter after regrafting. If these expectations can be realized, then the possibility of successfully establishing a "new" and functional endothelium on recipient corneas destined for clinical grafting may well be brought to fruition in the not-too-distant future.     

Effect of growth factors with dexamethasone on healing of rabbit corneal stromal incisions

Treatment of rabbit corneal wounds with topical corticosteroid retards both epithelial regeneration and healing of penetrating stromal wounds. Currently, no clinical agent is available which accelerates the rate of stromal wound healing. Epidermal growth factor (EGF, 0.5 mg ml-1), fibroblast growth factor (FGF, 20 micrograms ml-1), and insulin (0.5 mg ml-1) were tested for their ability to accelerate healing of totally penetrating wounds in rabbit corneas when the hormones were administered alone or in combination with dexamethasone (1 mg ml-1). After 5 days of treatment with eye drops, the tensile strengths of corneal wounds treated with EGF (54 +/- 4 g mm-1) or treated with EGF and dexamethasone (32 +/- 9 g mm-1) were significantly higher than the tensile strengths of corneal wounds treated with only saline vehicle (3 +/- 1 g mm-1) or dexamethasone (1 +/ 0 g mm-1) (P less than 0.001). The combination of dexamethasone with EGF significantly (P less than 0.025) reduced the strength of corneal wounds compared to treatment with EGF alone. Similarly, the tensile strength of corneal wounds after 5 days of insulin treatment alone (28 +/- 8 g mm-1) or in combination with dexamethasone (25 +/- 7 g mm-1) was significantly increased compared with saline- or dexamethasone-treated corneas (P less than 0.001). In the absence of dexamethasone, EGF increased the tensile strength of corneal wounds significantly better than insulin (P less than 0.01). However, when EGF or insulin were given in combination with dexamethasone there was no significant difference between the tensile strength produced by the peptide hormones. In comparison to the tensile strength of corneal wounds treated by EGF or insulin, treatment with FGF alone (5 +/- 4 g mm-1) or in combination with dexamethasone (2 +/- 1 g mm-1) produced poor wound healing. The in vitro actions of EGF or FGF alone or in combination with dexamethasone were tested for ability to stimulate [3H]-thymidine incorporation into pure cultures of human corneal fibroblasts (HCF) in defined culture medium. EGF (5 mM) or FGF (100 ng ml-1) alone stimulated [3H]-thymidine incorporation approximately 2.5-fold compared to control cultures, whereas in combination with dexamethasone (10 nM), the stimulatory action of FGF, but not EGF, was abolished. Dose-response curves indicated that HCF in culture were very sensitive to EGF, insulin, and FGF with maximum stimulation of [3H]-thymidine incorporation occurring at approximately 1 nM for EGF and insulin and at 100 micrograms ml-1 for FGF. Binding of 125I-EGF to HCF reached maximum after 2 hr at 37 degrees C and was specific, saturable, and of high affinity (half saturation at 1 nM). (ABSTRACT TRUNCATED AT 400 WORDS)     

人脐带血清器官培养液保存猪角膜的实验研究

目的 观察胎牛血清器官培养液和人脐带血清器官培养液对猪角膜内皮细胞形态学、组织学、超微结构、酶活性及代谢等的影响。方法 器官培养方法：4周以内31℃密闭培养,之后脱水24h。选择猪眼113只,其中100只角膜分为两组进行配对器官培养保存。第1组(50只角膜)：应用培养液Ⅰ(含10％胎牛血清);第2组(50只角膜,第1组的对侧角膜)：应用培养液Ⅱ(含10％人脐带血清)。13只角膜作为正常对照。器官培养每周每组各取出12只角膜进行内皮细胞形态学分析、HE染色、酶组织化学染色。保存2周、4周时行扫描电镜检查。检测保存前后培养液的pH值和葡萄糖、乳酸浓度。器官培养过程中行微生物学检测。结果 器官培养期间角膜内皮细胞单层保持完整,多形性增加,两组之间角膜内皮细胞密度、细胞面积的变异系数和六边形细胞比例在保存4周内差异无显著意义。保存4周的猪角膜与正常猪角膜相比,平均内皮细胞丢失率第1组为10．98％,第2组为10．85％。两组角膜器官培养后的组织学、超微结构、酶活性无明显区别。扫描电镜显示内皮细胞层完整,细胞形态改变。酶组织化学染色显示上皮、内皮细胞酶活性旺盛,基质细胞的酶活性随保存时间的延长而降低。角膜代谢状态良好。器官培养液污染率为6％。结论 两种器官培养液均可以保持角膜内皮活性达4周,推测人脐带血清能够替代胎牛血清作为角膜器官培养液的成分。(中华眼科杂志,2004,40：533-538)     

Contact lenses as a drug delivery device for epidermal growth factor in the treatment of ocular wounds

Background: This work was conducted to investigate the uptake and release of epidermal growth factor (EGF) from hydrogel contact lenses and to determine whether the released protein would be therapeutically active in a rabbit corneal epithelial defect model of ocular trauma, prior to use in humans. Methods: The uptake and release of EGF from hydrogel contact lens materials were determined by high‐pressure liquid chromatography. Contact lenses composed of vasurfilcon A or lotrafilcon A (containing silicone) were incubated in a source solution containing 0.4 ppm EGF for seven hours. To determine the kinetics of drug uptake into the contact lens matrix, drug concentration in the source solution was measured at zero, one, 60, 240 and 420 minutes. To determine the kinetics of release, loaded contact lenses were immersed in a recipient solution of phosphate‐buffered saline. Therapeutic activity in vivo was investigated by placing prepared lenses on the surface of abraded corneas of New Zealand White rabbits, with abraded corneas of contralateral eyes used as controls. Control eyes were treated with contact lenses placed in saline for injection. Wound closure was assessed hourly. Results: Uptake and release of EGF were demonstrated for vasurfilcon A but not lotrafilcon A contact lens materials. The retention time of EGF released from vasurfilcon A contact lenses was similar to control EGF not exposed to contact lens polymers. The greatest adsorption of EGF into the lens material occurred within approximately 120 minutes, with a flattening of the rate of uptake thereafter. Abraded eyes in rabbits showed a significantly higher overall healing rate for EGF‐treated contact lenses compared with control eyes (p < 0.0001). Conclusions: EGF can be delivered from some but not all hydrogel materials. Lens materials composed of silicone may not be useful for delivering EGF to the eye. EGF‐treated contact lenses may be a useful device to facilitate healing of ocular wounds.     

Endothelial cell density in porcine corneas after exposure to hypotonic solutions

Purpose To evaluate exposure to sucrose solution (1.8%) and hypotonic balanced salt solution (BSS) for its effects on endothelial cell density of porcine corneas.Methods Two groups of central discs from pig corneas were organ-cultured for 24 h. Twelve corneas per group were exposed to sucrose solution (1.8%) or hypotonic BSS for 4 min each. The paired corneal discs were not treated and served as controls. After further organ culture with and without dextran for 48 h, corneal endothelium was stained with alizarin red and examined by light microscopy. The endothelial cell densities were determined manually on three central images.Results The endothelial cell density differed significantly between corneas exposed to sucrose and the control corneas (3982±382 cells/mm² and 4360±331 cells/mm² respectively, and 3876±364 cells/mm² versus 4374±168 cells/mm² respectively with 6% dextran). In contrast, the endothelial cell density did not differ significantly between corneas exposed to hypotonic BSS and the control corneas (4374±296 cells/mm² and 4317±193 cells/mm² respectively, and 4348±151 cells/mm² versus 4426±175 cells/mm², respectively with 6% dextran).Conclusions Exposure to 1.8% sucrose for 4 min induces a significant endothelial cell loss of 10% on average, whereas exposure to hypotonic BSS did not significantly influence the endothelial cell density.Presented in part at the annual meeting of the Deutsche Opthalmologische Gesellschaft (DOG), Berlin, 2005.     

Value of two mortality assessment techniques for organ cultured corneal endothelium: trypan blue versus TUNEL technique

BACKGROUND/AIM: It is known that trypan blue staining is not a good predictor of loss of corneal endothelial cells (ECs) during organ culture. As it is primarily an indicator of membrane integrity, it would also not be expected to identify ECs undergoing apoptosis. The aim of this study was to determine the ability of the in situ TdT dUTP mediated nick end labelling (TUNEL) technique to detect cell death in the corneal endothelium caused by apoptosis during organ culture, compared with conventional vital staining with trypan blue. METHODS: 31 human corneas were organ cultured at 31C for 3-35 days. Staurosporine was used to induce apoptosis in five control corneas. The endothelium was assessed by trypan blue and by the in situ TUNEL technique. The percentages of trypan and TUNEL positive ECs were compared. Their links with sex, donor age, time from donor death and organ culture, initial and final EC density and cell loss were studied. RESULTS: TUNEL stained ECs were observed in all corneas. TUNEL positive ECs were mostly located either in corneal folds or at the periphery of corneal folds showing central shedding. The mean percentage of cell death at the end of storage, assessed by the trypan blue technique, was 1.47% (SD 2.63, range 0.03-12); assessed by the TUNEL technique it was 12.7% (SD 16.4 range 0.6-65.5). There was a significant correlation between the two techniques (r = 0.7, p<0.001). The percentage of TUNEL stained ECs was correlated negatively with EC density at the end of storage (r = -0.47, p <0.005) and positively with percentage EC loss during storage (r = 0.46, p < 0.05). CONCLUSION: This study demonstrates that organ cultured corneas systematically carry non-viable ECs that are implicated in cell death by apoptosis and go undetected when trypan blue staining is used. Because the in situ TUNEL assay detects earlier events in the cell death process than does trypan blue, it should be used to quantify endothelial viability, especially for experiments with new storage media.     

Collagen ultrastructural changes during stromal wound healing in organ cultured bovine corneas

Corneal collagen ultrastructural changes occur during the healing process. The present study was designed to compare collagen ultrastructural changes after trephine wounding or flap creation. Bovine corneas were injured and maintained in organ culture for up to 4 weeks. Samples were removed from culture at 0, 1, 2, 3 and 4 weeks and snap frozen in liquid N₂. X-ray scattering was used to measure changes in collagen interfibrillar spacing, intermolecular spacing and fibrillar diameter. Some samples were fixed in 10% Neutral Buffered Formalin solution and wax embedded for immunohistochemistry to monitor myofibroblast differentiation in corneal flaps. Swelling effects (i.e. changes in interfibrillar spacing) were more severe in trephined corneas than in those with stromal flaps. Collagen fibrillar diameter remained normal in the periphery of injured corneas, but increased significantly in areas within and around the wound in trephined samples and in the epithelial incision site in corneal flaps. Intermolecular spacing was unchanged in all samples. In the flaps, αSMA expression was only detected in an area adjacent to the epithelial plug, and cell numbers gradually increased during the culture. We conclude that stromal swelling is more rapid for trephine-wounded corneas than in stromal flaps, indicating that the intensity of the corneal healing response depends on the type of injury.     

Einfluss des Transportes auf organkultivierte Hornhäute

BACKGROUND: To investigate the influence of transport on the quality of corneas in organ culture, based on the vitality of the corneal endothelium. METHODS: Transport was simulated for 222 porcine corneal disks. These were placed in standard transportation containers filled with organ culture medium II, kept in an incubator and then shaken on a laboratory shaker. RESULTS: Agitated corneas at all acceleration rates always showed less endothelial cell damage than corneas kept motionless. The best condition was found after maximum accelerations of 0.10 g and 0.72 g. Damage consisted predominantly of disseminated cell loss and circular cell damage. A storage temperature of 37 degrees C caused most harm to the endothelium. CONCLUSION: The reduction in endothelial damage found in corneas after agitation can be attributed to a better distribution of nutrients in the transportation container. Assuming transferability, a better quality of human grafts can be achieved by inducing slight motions of corneas in organ culture.