Topical fibronectin and corneal epithelial wound healing in the rabbit

Commercial amniotic membrane extract for treatment of corneal ulcers in adult horses

BACKGROUND

Amniotic membrane extract enhances the rate of epithelialisation after corneal ulceration in several species but has not been studied in the equine cornea.

OBJECTIVES

To evaluate the effect of amniotic membrane extract on re-epithelialisation of equine corneal ulcers compared with ulcers treated with antibiotic, antifungal and mydriatic medical therapy alone, and to evaluate equine corneal healing after experimentally induced superficial ulceration.

STUDY DESIGN

Masked, randomised, controlled experimental trial.

METHODS

Superficial, 8 mm corneal ulcers were created bilaterally in each horse. One eye was treated with amniotic membrane extract and the opposite was control. Both eyes were treated with medical therapy. Treatment eyes received amniotic membrane extract, and control eyes received the amniotic membrane extract vehicle. Ulcers were stained with fluorescein and photographed in 12-hour increments until completely healed. Ulcer surface area was determined by analysing photographs with ImageJ. A mixed linear model was used to compare ulcer surface area and hours until healing between treatment groups. A regression model was also used to calculate corneal re-epithelialisation rate over time.

RESULTS

Regardless of therapy, healing occurred in two phases: an initial rapid phase of 0.88 mm² /hr (95% CI: 0.81-0.94 mm² /hr) for approximately 48-54 hours followed by a second, slow phase of 0.07 mm² /hr (95% CI: 0.04-0.09 mm² /hr). Most eyes healed within 135.5 ± 48.5 hours. Treatment (amniotic membrane extract vs. control) was not significantly associated with size of ulcers over time (P = .984). Discomfort was minimal to absent in all horses.

MAIN LIMITATIONS

Results achieved experimental studies may differ from outcomes in the clinical setting.

CONCLUSIONS

There was no significant difference in healing rate with addition of amniotic membrane extract to medical therapy for equine superficial corneal ulcers. A biphasic corneal healing process was observed, with an initial rapid phase followed by a slow phase. Further study will be needed to determine whether amniotic membrane extract will be helpful for infected or malacic equine corneal ulcers.

Effects of Transforming Growth Factor-Beta 2, Interleukin 6 and Fibronectin on Corneal Epithelial Wound Healing

Purpose

The aim of this study was to compare the effects of topically applied transforming growth factor-beta 2 (TGF-beta 2) and interleukin 6 (IL-6), alone and combined with fibronectin, on the rate of corneal wound healing in rabbits.

Methods

Twenty-eight rabbits were used for the experiment. After the right eye of each rabbit was debrided with n-heptyl alcohol, the animals were divided into four treatment groups (six rabbits per group) and one control group (four rabbits). The debrided eyes were treated, beginning immediately after wounding and continuing every 2 hours from 8 a.m. to 8 p.m. for 48 hours. Group 1 received TGF-beta 2; group 2 IL-6; group 3, TFR-beta 2 and purified fibronectin; group 4, IL-6 and fibronectin; control group, balanced salt solution. At set intervals each eye was stained with fluorescein and photographed; epithelial defects were measured with a computer-assisted digitizer. The healing rate was calculated by linear regression analysis.

Results

The mean healing rates in groups 1, 2, 3, 4, and controls were respectively 1.65 ± 0.16, 1.68 ± 0.11, 1.99 ± 0.12, 2.23 ± 0.09, and 0.93 ± 0.18 mm2/h. Mean epithelial healing rates for all drug-treatment groups were significantly faster than controls. The healing rates of groups 3 and 4 were significantly faster than groups 1 and 2.

Conclusions

We conclude that cytokines, in combination with extracellular matrix proteins, facilitate corneal epithelial wound healing in vivo, possibly by making corneal epithelial cells more sensitive to fibronectin receptors.

Expression of Fibronectin Isoforms Bearing the Alternatively Spliced EIIIA, EIIIB, and V Segments in Corneal Alkali Burn and Keratectomy Wound Models in the Rat

PURPOSE

To better understand the healing process in the wounded cornea, fibronectin (FN) isoforms bearing the alternatively spliced EIIIA, EIIIB, and V segments (EIIIA+, EIIIB+, and V+ FNs) were evaluated in alkali burn and keratectomy wound models in the rat.

METHODS

Alkali burn or keratectomy wounds (both 2 mm) were created, and corneas were harvested at various time points and analyzed by indirect immunofluorescence using antibodies specific for the EIIIA, EIIIB, and V segments as well as for the total pool of FN (total FN).

RESULTS

There was minimal staining for any variety of FN in the epithelium or basement membrane zone (BMZ) in normal cornea, but each antibody produced granular staining in the stroma. Bright staining for V+ and total FNs was evident at the denuded stromal surface 1 day following keratectomy. In contrast, staining for EIIIA+ and EIIIB+ FNs was negligible at 24 hours but appeared on the wound surface under the migrating unstained epithelium by the second day. BMZ staining for FN then gradually subsided, such that there was little or no staining by 6 weeks. In contrast, alkali burn wounds exhibited very little BMZ staining throughout the time course. Although there was preferential staining of the anterior aspect of Descemet membrane by anti-EIIIA and anti-EIIIB antibodies under normal conditions, the staining intensity of the anterior and posterior aspects became similar following corneal wounding.

CONCLUSION

Deposition of EIIIA+ and EIIIB+ FNs in the BMZ of the keratectomy wound occurs more slowly than deposition of V+ and total FNs. EIIIA+ FN is expressed in a distribution that overlaps with that previously described for the alpha 9 integrin subunit following corneal debridement, suggesting that EIIIA-alpha 9 interactions could occur during corneal wound healing. In contrast, the relative lack of FN deposition in alkali burn wounds suggests that proteolytic degradation of FN may occur; and this, along with impairment of new FN synthesis because of cellular damage, could play a role in the high prevalence of recurrent epithelial erosions in alkali-wounded corneas.

Electric field-directed cell motility involves up-regulated expression and asymmetric redistribution of the epidermal growth factor receptors and is enhanced by fibronectin and laminin

Wounding corneal epithelium establishes a laterally oriented, DC electric field (EF). Corneal epithelial cells (CECs) cultured in similar physiological EFs migrate cathodally, but this requires serum growth factors. Migration depends also on the substrate. On fibronectin (FN) or laminin (LAM) substrates in EF, cells migrated faster and more directly cathodally. This also was serum dependent. Epidermal growth factor (EGF) restored cathodal-directed migration in serum-free medium. Therefore, the hypothesis that EGF is a serum constituent underlying both field-directed migration and enhanced migration on ECM molecules was tested. We used immunofluorescence, flow cytometry, and confocal microscopy and report that 1) EF exposure up-regulated the EGF receptor (EGFR); so also did growing cells on substrates of FN or LAM; and 2) EGFRs and actin accumulated in the cathodal-directed half of CECs, within 10 min in EF. The cathodal asymmetry of EGFR and actin staining was correlated, being most marked at the cell-substrate interface and showing similar patterns of asymmetry at various levels through a cell. At the cell-substrate interface, EGFRs and actin frequently colocalized as interdigitated, punctate spots resembling tank tracks. Cathodal accumulation of EGFR and actin did not occur in the absence of serum but were restored by adding ligand to serum-free medium. Inhibition of MAPK, one second messenger engaged by EGF, significantly reduced EF-directed cell migration. Transforming growth factor beta and fibroblast growth factor also restored cathodal-directed cell migration in serum-free medium. However, longer EF exposure was needed to show clear asymmetric distribution of the receptors for transforming growth factor beta and fibroblast growth factor. We propose that up-regulated expression and redistribution of EGFRs underlie cathodal-directed migration of CECs and directed migration induced by EF on FN and LAM.

In vitro model for corneal wound healing; organ-cultured human corneas

Healing of linear, non-perforating thermal burns was studied in 56 human corneas in an air/liquid organ culture system in serum free medium or in media supplemented with 10% fetal bovine serum, 10% human serum or 10% human plasma. The extent of epithelial wound healing was determined by measuring epithelial growth into the wound using digitized computer scanning of light micrographs of 1 micron sections. The cross-sectional area of this epithelial growth entering the wound was significantly greater for corneas incubated with either human serum (16,350 +/- 12,088 microns 2/day; p < 0.0001) or human plasma (20,571 +/- 12,276 microns 2/day; p = 0.0004) than for those incubated in serum free (1,784 +/- 1,957 microns 2/day) medium. There was no significant difference between epithelial growth in the serum free and fetal bovine serum supplemented (3,779 +/- 2,580 microns 2/day) media or between that in human serum and human plasma supplemented media. The thickness of the epithelium adjacent to the wound was greater in corneas cultured in fetal bovine serum supplemented media than in corneas cultured in the presence of human serum. Similarly, the build-up of epithelium at the wound edge for corneas in either serum free or fetal bovine serum supplemented media was significantly greater than for either human serum or human plasma supplemented media. The percentage of basal epithelial nuclei which incorporated bromodeoxyuridine (BrdU) increased during the first three days of culture when it reached a plateau. Comparison of paired wounded and unwounded corneas showed that wounding stimulated an increase in DNA synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Topical fibronectin ophthalmic solution in the treatment of persistent defects of the corneal epithelium. Chiron Vision Fibronectin Study Group

PURPOSE

We sought to evaluate the efficacy of topical fibronectin ophthalmic solution, containing 3.5 mg/ml of human fibronectin, in the treatment of persistent epithelial defects of the cornea.

METHODS

In a double-masked, randomized clinical trial, patients with a persistent, corneal epithelial defect of at least 14 days in duration, and at least 2 mm in width along the larger axis, were sought from the practices of 38 clinical investigators. After a 14-day washout period, 65 patients were randomly assigned to one of three treatment groups. One group (n = 20) received fibronectin drops; the second (n = 23) received drops of the vehicle from the fibronectin solution; and the third (n = 22) received a placebo.

RESULTS

After 21 days of treatment, there was no difference in percentage reduction of the corneal epithelial defect size; the average percentage of reduction of defect area ranged from 46.5% to 54.3%. Fibronectin treatment showed a beneficial effect for patients with larger baseline defects (10 mm2 or greater in area); however, no such effect was observed among patients with smaller defects. Defect duration before treatment had a significant effect on outcome (P = .007); defects of longer duration were less likely to decrease in size over the course of the study.

CONCLUSIONS

All three treatment groups showed similar reductions in defect size; therefore, this study provides no support for the efficacy of fibronectin treatment of persistent, corneal epithelial defects. Defect duration showed a negative association with reduction in defect size. Because strict control of topical applications during the washout and treatment periods resulted in beneficial responses, physicians should carefully consider the topical medications used by patients who have persistent, corneal epithelial defects.

Angiogenic activity of fibrin degradation products is located in fibrin fragment E

The source of angiogenic activity of fibrin degradation products has been sought in a series of experiments, applying degradation products from different types of fibrin and fibrinogen to the chick chorioallantoic membrane. The presence of platelets or fibronectin during clotting was not essential for activity, and neither was crosslinking. Fibrinogen degradation products were non-stimulatory, as was serum. Molecular sieve column chromatography indicated a range of active fragments. Admixture of active fibrin degradation products with antifibrin fragment E, but not D, antiserum neutralized activity. Preparations containing only fibrin fragment E retained activity. A commercial preparation of fibrinogen fragment E was inactive until treated with thrombin. These experiments point to fibrin fragment E being the source of angiogenic activity, with thrombin cleavage being the essential step in generating activity.

Epikeratophakia: histopathological and cultural study

Three epikeratoplasty buttons (one aphakic and two myopic) prepared by the freeze technique were removed two to nineteen months after surgery. A complete morphological and immunohistochemical study was performed on these buttons in order to gain insight into the reasons for epikeratophakia failure. Histopathological studies with light microscopy and scanning and transmission electron microscopy were performed. All three cases showed an anomalous process of re-epithelialization: in the first, the epithelium over the donor cap was almost completely absent, with many abnormalities; in the second, the epithelium was irregular, with a varying number of cell layers and poor adhesion between cells; in the third, the development of an epithelial cyst between the tissue lens and the cornea of the host caused the failure of the epikeratoplasty. The specimens were cultured 'in vitro' and the cells grown typed for HLA antigens. The antigen panel was the same as that of the host. Immunohistochemistry showed CD3- and CD8-positive cells in the stroma, proving the activity of T-suppressor lymphocytes in a cell-mediated immunoreaction.