Histochemical study of alkali-burned rabbit anterior eye segment in which severe lesions were prevented by aprotinin treatment

Urokinase down-regulation by aprotinin in rabbit corneal cells after photorefractive keratectomy

PURPOSE

To examine the effect of aprotinin eye drops on urokinase-type plasminogen activator (uPA) gene expression in rabbit corneal cells during wound healing after photorefractive keratectomy (PRK).

METHODS

Both eyes of 22 rabbits were subjected to PRK. One eye of each rabbit was treated with antibiotic eye drops five times while the contralateral eye was treated at the same time with antibiotic eye drops and a serine protease inhibitor. The animals were sacrificed at different time frames, and 2-4 rabbits were used for each time point. Half of each cornea was used for the determination of the amount of uPA mRNA after reverse transcription and real-time quantitative polymerase chain reaction, while frozen sections were prepared from the other halves for in situ zymography to detect uPA activity.

RESULTS

The level of uPA mRNA in corneal cells was markedly increased in corneal samples obtained hours after PRK. The time-dependent up-regulation of uPA mRNA was strongly dependent on the diameter of the area from which the epithelial cells were removed before the surgery. Independently of the time scale of uPA up-regulation, application of eye drops containing aprotinin significantly diminished the uPA expression. In situ zymography confirmed that aprotinin has also decreased overall uPA activity.

CONCLUSIONS

Aprotinin down-regulates uPA gene expression in corneal cells during the wound-healing phase after PRK.

The influence of various toxic effects on the cornea and changes in corneal light transmission

PURPOSE

Normal corneal hydration is necessary for the maintenance of corneal transparency. Damage of the corneal epithelium or endothelium by various external influences disturbs the mechanism by which the cornea maintains normal hydration and transparency. The cornea swells, and the corneal thickness increases, resulting in increased scatter and the development of corneal opacity. The transmission of light across the cornea is changed. The purpose of this study is to investigate spectrophotometrically the corneal light transmission under the influence of the various factors affecting the cornea.

METHODS

We developed a spectrophotometric method to measure the light transmission across the cornea under the influence of various factors affecting the cornea, such as treatment with 0.9% NaCl, saline, or phosphate buffered saline (PBS), solutions employed as placebo eye drops (negative controls) in experimental studies, agents toxic to the cornea, such as diluted acids or alkalis. The method distinguishes between changes in corneal light transmission caused by altered corneal thickness (the level of hydration) and changes resulting from other corneal disturbances which in turn affect corneal light transmission.

RESULTS

The results obtained show that the corneal light transmission is decreased following the application of toxic substances on the corneal surface. This decrease is highly dependent on the severity of the corneal injury evoked by individual noxes, and the resulting changes in corneal hydration and transparency.

CONCLUSIONS

The influence of various influences applied to the cornea, manifested as changes in corneal light transmission, can be measured using our spectrophotometric method with a high degree of sensitivity.

Experience with plasmin inhibitors

The involvement and role of the plasminogen activator-plasmin system in normal and pathological wound healing is reviewed. The methods currently available for demonstrating plasmin activity are briefly described. The article also reviews some other serine proteases potentially involved in pathological wound healing processes. The current ophthalmological therapeutic measures used to regulate tissue proteolysis are also described.

Dynamic analysis of chemical eye burns using high-resolution optical coherence tomography

The use of high-resolution optical coherence tomography (OCT) to visualize penetration kinetics during the initial phase of chemical eye burns is evaluated. The changes in scattering properties and thickness of rabbit cornea ex vivo were monitored after topical application of different corrosives by time-resolved OCT imaging. Eye burn causes changes in the corneal microstructure due to chemical interaction or change in the hydration state as a result of osmotic imbalance. These changes compromise the corneal transparency. The associated increase in light scattering within the cornea is observed with high spatial and temporal resolution. Parameters affecting the severity of pathophysiological damage associated with chemical eye burns like diffusion velocity and depth of penetration are obtained. We demonstrate the potential of high-resolution OCT for the visualization and direct noninvasive measurement of specific interaction of chemicals with the eye. This work opens new horizons in clinical evaluation of chemical eye burns, eye irritation testing, and product testing for chemical and pharmacological products.

Local suppression of IL-1 by receptor antagonist in the rat model of corneal alkali injury

Proinflammatory cytokines, including interleukin-1 (IL-1) have been implicated in the inflammation that follows corneal alkali injury. The purpose of this series of experiments was to test whether topically applied interleukin-1 receptor antagonist (IL-1ra) could suppress corneal inflammation and promote transparency after alkali injury. Alkali injury was induced on day 0 by application of 1N NaOH to both eyes of Wistar rats (n = 28). Immediately thereafter, eyes received either topical IL-1ra (20 mg ml(-1)) in 0.2% sodium hyaluronate or vehicle alone three times daily during days 0-14. Biomicroscopic features including corneal opacity and neovascularization were assessed using a standard grading scheme. Inflammation was quantified histologically. Corneas excised at day 3 and 7 (randomly selected six eyes in each group per time point studied) were homogenized, and levels of IL-1alpha, IL-1beta, IL-6, IL-8, IL-10, and RANTES were quantified by enzyme-linked immunosorbent assay. Epithelial wound healing was examined by computed analysis of fluorescein stained corneal photographs taken daily until day 14. According to these evaluations, eyes treated with IL-1ra maintained corneal transparency with minimal neovascular invasion. Additionally, corneal damage and cell infiltration were reduced on day 7 (infiltration cells were almost 40% decreased). All cytokine/chemokine levels in IL-1ra treated eyes were significantly lower at day 3, and IL-6 and IL-10 remained significantly lower at day 7 compared to vehicle-treated eyes. IL-1ra treatment retarded epithelial wound healing in the early stage (day 1-4); however, subsequently IL-1ra treated eyes had enhanced healing with full epithelial closure at nearly the same time point as vehicle-treated eyes (day 10). We conclude that local antagonism of IL-1 after alkali injury can significantly decrease corneal inflammation and lead to enhanced corneal transparency.

The application of histochemical methods to the age evaluation of skin wounds: experimental study in rabbits

Enzyme histochemical methods allow determination of wound age, especially in the range of a few hours, and are used to distinguish between postmortem and antemortem skin wounds. The methods are based on the determination of the presence and changes of the enzyme reaction in the wound area. Increased activity of nonspecific esterases was observed approximately 1 hour after wounding and was followed by an increase in adenosine triphosphatase at approximately 2 hours and alkaline phosphatase at approximately 3.5 hours. Maximum enzyme activity was reached for nonspecific esterases at 24 hours, for adenosine triphosphatase at 20 hours, and for alkaline phosphatase at 32 hours after wounding.

The functions of exogenous and endogenous laminin-5 on corneal epithelial cells

Recent evidence suggests that the basement membrane not only separates basal cells from Bowman's layer, but also has a crucial role in the proliferation, differentiation and migration of corneal epithelial cells. The basement membrane is composed of a mixture of matrix components including collagens, laminins and heparan sulfate proteoglycans. In these extracellular matrixes, laminin is a major component of the basement membrane. Of 11 laminin isoformes, laminin-5 is a variant, composed of three nonidentical subunits alpha3, beta3, gamma2 and is a major component of the corneal basement membrane. However, little is known about the interactions of laminin-5 with corneal epithelial cells. In this study, we investigated the functions of laminin-5 on SV-40 transfected human corneal epithelial cells (HCE cells). We also revealed different functions between exogenous and endogenous laminin-5 on HCE cells. Laminin-5 is synthesized initially as a 490 kDa molecule that undergoes specific processing to cleavaged isoforms after being secreted. The alpha3 subunit is processed from 200-190 kDa to 160 kDa/145 kDa. The gamma2 subunit is processed from 150 kDa to 105 kDa/80 kDa. The beta3 subunit (140 kDa) is not processed. Exogenously added laminin-5 (soluble form) in this study was purified from a serum-free, conditioned medium of a human gastric carcinoma cell line STKM-I. This soluble laminin is a processed isoform containing alpha3 (160 kDa), beta3 (140 kDa) and gamma2 (105 kDa) chains. On the other hand, immunocytochemical analysis showed that HCE cells themselves secreted laminin-5 endogenously. Western blotting analysis revealed that HCE cells initially produced unprocessed isoform containing 190 kDa alpha3, 140 kDa beta3 and 150 kDa gamma2 chains and that after being secreted, the alpha3 chain was processed to 160 kDa/145 kDa and the gamma2 chain was processed to 105 kDa. Initially we investigated the functions of exogenous (processed) laminin-5 on HCE cells. Exogenously added laminin-5 strongly promoted cell adhesion via alpha3beta1 integrin, cell spreading, assembly of hemidesmosomes and mildly inhibited cell migration. Next we estimated the effect of endogenous (unprocessed) laminin-5 on HCE cells. Using an anti laminin-5 monoclonal antibody (mAb) or anti integrin alpha3beta1 mAbs, the blocking of the interaction between endogenously secreted laminin-5 and HCE cells caused strong inhibition of cell migration. Integrin alpha3beta1 and alpha6beta4 were expressed in HCE cells. These integrins are receptors of laminin-5. But, anti integrin alpha6beta4 mAbs did not have any blocking ability against cell migration. These results indicated that endogenous (unprocessed) laminin-5 has a crucial role in cell migration on HCE cells via alpha3beta1 integrin. In conclusion, structural differences between exogenous (processed) and endogenous (unprocessed) laminin-5 regulated their functions on HCE cells. Exogenously added laminin-5 strongly promoted cell adhesion, cell spreading and assembly of hemidesmosomes. Endogenously secreted laminin-5 had a crucial role in cell migration. In the future, processed soluble laminin-5 could be a useful drug for the prevention of recurrent corneal erosion, and unprocessed soluble laminin-5 could be applied for the treatment of prolonged corneal epithelial defects.

Toxicity of pentoxifylline on monolayers of highly proliferative cells of epithelial origin

Interest in pentoxifylline has been recently reawakened owing to its suppressive effect on cell cytokine production. In this capacity, it may be of value as a routine supplement for culture media containing donor corneas. The purpose of the present study was to evaluate the toxic effects of pentoxifylline on two standardized cell lines of epithelial origin. Vero and Chang cells were incubated with various concentrations of pentoxifylline. Acute toxicity (4 hr) was assessed by monitoring the permeability of cells to propidium iodide; chronic toxicity (7 days) was determined by monitoring the effect of pentoxifylline on esterase activity and cell proliferation. The viability of cells was also assessed by microscopic inspection. Signs of acute toxicity became manifest at a pentoxifylline concentration of 100 mg/l in both Chang and Vero cells. Indications of chronic toxicity were observed at a drug concentration of 10 mg/l in Chang cells but at 1 mg/l in Vero ones. Proliferation was suppressed at pentoxifylline concentrations of 100 mg/l and 10 mg/l in Chang and Vero cells, respectively. Degenerative morphological changes were observed at a drug concentration of 100 mg/l in both cell types. At a concentration of 0.1 mg/l, pentoxifylline elicited no signs of acute or chronic toxicity in either Chang or Vero cells. At this dose, the drug is therefore unlikely to have deleterious effects on cultured donor corneas.

Progressive ataxia, myoclonic epilepsy and cerebellar apoptosis in cystatin B-deficient mice

Loss-of-function mutations in the gene (CSTB) encoding human cystatin B, a widely expressed cysteine protease inhibitor, are responsible for a severe neurological disorder known as Unverricht-Lundborg disease (EPM1). The primary cellular events and mechanisms underlying the disease are unknown. We found that mice lacking cystatin B develop myoclonic seizures and ataxia, similar to symptoms seen in the human disease. The principal cytopathology appears to be a loss of cerebellar granule cells, which frequently display condensed nuclei, fragmented DNA and other cellular changes characteristic of apoptosis. This mouse model of EPM1 provides evidence that cystatin B, a non-caspase cysteine protease inhibitor, has a role in preventing cerebellar apoptosis.

Polymorphonuclear leukocyte cells and elastase in tears

PURPOSE

To characterize the effects that mode of sampling and overnight eye closure have on the nature of caseinolytic activity recovered in tear fluid.

METHODS

Reflex, open and closed (R, O and C) eye tear fluids were collected by microcapillary tubes or from the inferior formix by Schirmer strip. Microcapillary collected samples were centrifuged and recovered cells cytochemically characterized and probed by immunofluorescence microscopy, or alternatively extracted in acidic PBS. Tear supernatants, pellets and Schirmer strip extracts were subjected to casein zymography or SDS-PAGE and immunoprobed for plasmin/plasminogen. To identify caseinolytic activity, samples were immunoprecipitated with antibodies to plasmin/plasminogen or to elastase, and the immunoprecipitated materials were subjected to zymographic analysis.

RESULTS

Immunoblot assays revealed R and O samples contained low levels of plasminogen (approximately 1.1 micrograms/ml) and only trace levels of plasmin (< 0.1 ng/ml). Insufficient levels of caseinolytic activity were present to allow zymographic detection. Cytochemical analysis revealed that R and O pellets consisted almost exclusively of desquamated epithelium. Immunoblot analysis revealed that C fluid was associated with an increase in plasminogen and its partial conversion to plasmin (approximately 3.2 ng/ microliter), high molecular weight covalent complexes and degradative products. Zymographic analysis disclosed much greater caseinolytic activity than could be attributed to plasmin or its cleavage products. This consisted primarily of three bands (30-26 kDa) which were identified as polymorphonuclear leukocyte (PMN) cell elastase based on size and antigenicity. This is derived from PMNs recovered from the C pellet. Elastase could also be recovered from Schirmer strips from 90% of donors, provided that the strips were extracted in sample loading buffer. The activity was restricted to the portion of the strip that had been in contact with the ocular tissue.

CONCLUSIONS

The main source of caseinolytic activity in C fluid is elastase. This arises from PMNs that undergo recruitment, activation and degranulation in the C environment. In contrast, the elastase recovered in Schirmer strip extracts is derived from intact PMNs that adhere to the strip during sample collection. This would suggest that PMN cells undergo a low level of recruitment into the open eye environment.

The damaging effect of UV rays below 320 nm on the rabbit anterior eye segment. II. Enzyme histochemical changes and plasmin activity after prolonged irradiation

Prolonged irradiation of the rabbit eyes with UVB rays (312 nm) caused serious enzymatic disturbances in the cornea and lens and the development of an inflammatory reaction in the whole anterior eye segment, particularly in the cornea. In the corneal stroma many inflammatory cells with high activities of acid glycosidases and lysosomal proteases were present. This was accompanied with significantly elevated plasmin activity in the tear fluid (1.6 IU/ml). Plasmin appeared also in the aqueous humour (0.8 IU/ml). For the treatment of these changes catalase (1 mg/1 ml saline), aprotinin (100 micrograms/1 ml saline) and catalase-aprotinin mixture (1:1) were applied on the eye surface during irradiation. The catalase-aprotinin mixture was most efficient and decreased plasmin activity in the tear fluid and diminished disturbances of the anterior eye segment. Obviously both, active oxygen species and elevated plasmin activity in the tear fluid contribute to the damage of the anterior eye segment and development of intracorneal inflammation after irradiation of the eye with UVB rays.

Biochemical and histochemical studies of plasminogen activator of urokinase type (u-PA) activity. I. A simple rapid semiquantitative fluorescent method for its detection in the tear fluid

A simple rapid fluorescent method for the detection of plasminogen activator activity of urokinase type (u-PA) in the tear fluid is described. Small filter paper punches were soaked in the substrate solution (Z-Gly-Gly-Arg-trifluoromethylcoumarinyl-7-amide, 1 mg/1 ml) and aprotinin 100 micrograms/1 ml) dissolved in 0.1 M Tris-HCl buffer, pH 7.2 and dried. The dried punches were soaked with tears (by direct contact of the punch with the site where the activity should be assessed or by dropping of 3-5 microliters of tears collected by a glass micropipette). The punches were incubated in a thermostat (37 degrees C) together with punches containing a known u-PA activity (calibrated punches) in preheated (37 degrees C) Petri dishes. In 1 min intervals (during the first 15 min) and in 5 min intervals thereafter the probes were exposed to UV light, and the time of the first appearance of a bright yellow fluorescence was recorded. In punches containing 5 IU u-PA activity fluorescence appeared after 2 min incubation; 2.5 IU were detected after 5 min, 1.25 IU after 15 min, 0.625 IU after 30 min, 0.313 IU after 60 min, 0.156 IU after 90 min, and 0.078 IU after 120 min incubation. This simple method is recommended for use particularly in clinical laboratories. It enables e.g. to obtain a rather quick information about the urokinase activity in the tear fluid and to start the treatment with an appropriate inhibitor, if necessary.

The histochemical pattern of mechanically or chemically injured rabbit cornea after aprotinin treatment: relationships with the plasmin concentration of the tear fluid

Plasmin, a serine protease, was recently found to be involved in corneal ulcerative processes in humans and rabbits. In our experiments, plasmin activity was found in the tear fluid after mechanical and chemical damage of the rabbit cornea, such as de-epithelization and burning with alkali. The plasmin concentrations in the tear fluid were dependent on the severity of injury. The highest plasmin activity (2.0-3.0 micrograms ml-1) occurred after severe alkali damage to large areas of the cornea, and the lowest activity (0.4-1.0 micrograms ml-1) after mechanical injury (de-epithelization). Plasmin concentrations up to 1.0 micrograms ml-1 were associated with increased activities of lysosomal hydrolases in epithelial cells and keratocytes beneath the epithelium. Plasmin activities increased as the inflammatory reaction developed. When plasmin activity in the tear fluid was higher than 1.0 micrograms ml-1, inflammatory cells were found in the corneal stroma. Levels of 1.5-2.0 micrograms ml-1 were connected with higher numbers of inflammatory cells (particularly polymorphonuclear leukocytes) with increased activities of lysosomal hydrolases. Very high plasmin activities (2.5-3.0 micrograms ml-1) accompanied corneal ulcerative processes. The local application of aprotinin (Trasylol, Bayer), an inhibitor of plasmin, and also of some other proteases, was found to be necessary for the healing of severe corneal injuries in which highly elevated plasmin activity in the tear fluid and inflammatory cellulization of the cornea occurred (severe damage).(ABSTRACT TRUNCATED AT 250 WORDS)

Wound healing of the ocular surface

Wound healing is a complex, long-lasting regulatory sequence that involves expression of a number of genes, which are active during the individual's development. Some of the phenomena differ from normal tissue turnover and growth only quantitatively. This article reviews the current data on corneal wound healing, with particular reference to mesenchymal matrix proteins and their integrin receptors, to growth factors and to proteolytic enzymes. Some inflammatory mediators are also discussed. The theoretical basis for therapeutic interventions is also discussed briefly, in the light of present knowledge.

Histochemical changes in the rabbit cornea and plasmin activity in the tear fluid during contact lens wear. Favourable influence of protease inhibitors (aprotinin, PC5, elastatinal)

Plasmin activity in the tear fluid of the rabbit eye was examined during the wearing of soft contact lenses (SCL) and compared with the occurrence of corneal disturbances assessed in cryostat sections. Plasmin activity was determined with a semiquantitative method using dry punches of filter paper previously soaked in 0.1 M Tris-HCl buffer solution containing mmol/l D-Val-Leu-Lys-FCA (trifluoromethylaminocoumarine), pH 7.2. Punches were applied to the corneal surface for 5 s (tear collection) and incubated in wet chamber. The time of appearance of the bright yellow fluorescence in UV light was recorded and taken as a measure of plasmin activity. For calibration punches soaked in solutions containing plasmin in various concentrations, and processed in the same manner were used. Changes in the cornea were examined histochemically using methods of choice for acid glycosidases, proteases, dehydrogenases, and Na(+)-K(+)-ATPase. SCL with high and low water content were worn in rabbits in 1, 2, 4, 7, 14, 21 and 28 days. Decreased activity of Na(+)-K(+)-ATPase, GGT, and SDH in the corneal endothelium and epithelium were not accompanied by detectable plasmin activity in the tear fluid. Pronounced damage of the corneal epithelium (increased activities of acid glycosidases, acid proteases, LDH, markedly decreased activity of SDH) was accompanied by low concentration of plasmin (0.4-1.0 micrograms/ml) in the tear fluid. Middle activity of plasmin (1.0-2.0 micrograms/ml) was detectable when PMNs were present in the corneal stroma. High plasmin activity (2.0-3.0 micrograms/ml) correlated with corneal ulceration and vascularization.(ABSTRACT TRUNCATED AT 250 WORDS)

Ocular irritation leads to the appearance of proteolytic activity in the aqueous humor

Aqueous humor (AH) collected from healthy eyes of man and rabbit was analysed for proteolytic activity using a casein-agar assay. Normal AH collected during surgery or rabbit AH aspirated before ocular irritation contained no caseinolytic activity. In rabbits, mechanical irritation of the iris and subconjunctival as well as intracameral injection of capsaicin led to ocular irritative response. AH samples collected after such manipulation contained a considerable caseinolytic activity. On the other hand, anterior chamber puncture alone did not seem to induce elevation of caseinolytic activity in AH. The clinical significance of this phenomenon and the mechanisms behind it are discussed.

Beneficial effect of sodium sucrose-sulfate on the ocular surface of patients with severe KCS in primary Sjögren's syndrome

Sucralfate (aluminium sucrose-sulfate), a well known gastric mucosal protectant, has been tested topically on 22 patients (20 females and 2 males) suffering from primary Sjögren's syndrome. Median treatment period was 6 months (range 1-19 months). Statistically significant improvement in the ocular surface condition was found judged from the reduction in Rose-Bengal score (P less than or equal to 0.00005). The beneficial effect appeared within the first 1-4 months of treatment. No adverse side effects were encountered.