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1From the Department of Ophthalmology, Eberhard-Karls University Tübingen, Tübingen, Germany; and the 2Department of Ophthalmology, University of Wroclaw, Wroclaw, Poland.
| Abstract |
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METHODS. Glaucoma filtration surgery, similar to that performed in clinical practice, was performed on 35 chinchilla rabbits (ChBB:CH). The animals received a unilateral subconjunctival injection of decorin (40100 µg) or the vehicle alone before surgery and at different time intervals thereafter. Antifibrotic efficacy was established by clinical response and histologic examination. The animals were killed on day 14, and the eyes processed for histology.
RESULTS. Both the vehicle and the decorin solution were well tolerated. No adverse effects such as inflammation or blurring of the optical media were observed. Conjunctival scarification occurred within 1 week in the control groups but was suppressed in the experimental groups. The intraocular pressure correlated with the fibrotic process and reached normal levels within 7 days after surgery in control animals, but remained significantly (P < 0.001) reduced in the experimental groups. Histologic examination of the surgical area 14 days after surgery disclosed massive fibrosis in the control animals, but little deposition of extracellular matrix in the experimental groups.
CONCLUSIONS. The data of this pilot study suggest that perioperative subconjunctival decorin applications significantly affect conjunctival scarring and surgical outcome of glaucoma filtration treatments in rabbits.
Inspired by these studies we wanted to analyze whether a naturally occurring TGF-ß inhibitor, decorin,25 could be used instead of the potentially immunogenic polyclonal antibodies23 or the more demanding recombinant human anti-TGF-ß antibodies.24 The objectives of this study were to investigate the use of subconjunctival decorin in a rabbit model of glaucoma filtration surgery and to assess the antiscarring potential, the safety, and the tolerance of this TGF-ß inhibitor.
| Materials and Methods |
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Animals
All experiments were performed with female chinchilla bastard rabbits (ChBB:CH), 3 to 6 months old and weighing 1.5 to 2.5 kg. Animals were obtained from Charles River Laboratories (Sulzfeld, Germany) and acclimatized for 1 week before the experiments started.
Surgical Procedure
Surgery was performed on the right eye only under general anesthesia with intramuscular injections of ketamine (Ketanest; Parke Davis, Berlin, Germany) and xylazine (Rompun; Bayer, Leverkusen, Germany) and local anesthesia with oxybuprocaine drops (Novesine 0.4%; Novartis, Nürnberg, Germany). Briefly, after a lid speculum was placed, a partial-thickness 8-0 silk corneal traction suture (Ethikon, Edinburgh, UK) was placed superiorly, and the eye was pulled down. A peritomy at 5 mm limbus distance was used to form a limbus-based conjunctival flap. A limbus-based rectangular (2.5 x 2.5-mm) scleral flap was outlined with a steel blade and carefully dissected. A trephine (diameter, 1.5 mm) was then used to create the entry into the anterior chamber at the surgical limbus. Consequently, the trephine block of tissue was excised and a peripheral iridectomy performed. Because of the known aggressive wound healing in this model, no suturing of the scleral and conjunctival flap was necessary. On three consecutive days after surgery, each animal received once-a-day drops containing a steroid and an antibiotic (Dexamytrex; Dr. Mann Pharma, Berlin, Germany).
Preparation and Administration of Decorin
Decorin (D-8428; Sigma-Aldrich, Steinheim, Germany) was dissolved in physiologic saline (Balanced Salt Solution [BSS]; Pharmacia, Groningen, The Netherlands) at 0.4 or 1 mg/mL. The saline solution alone served as the vehicle control. Both were administered with animals under general and topical anesthesia. A 30-gauge needle was used to inject 100 µL of either the decorin solution or the vehicle alone. The needle was placed at the nasal margin of the superior rectus muscle, so that a visible bleb was formed on the supranasal quadrant (Fig. 1) .
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= 0.9 and relevant difference
= 0.2, the sample size was calculated for a two-tailed test (n = 5). The groups were subdivided as shown in Table 1 and described in the following (in all groups, n = 5): Group A was a control group of animals that received subconjunctival injection of decorin (100 µg) only. Group B was a control group that underwent filtration surgery only. Group C, the third control group, received surgery and the most frequent application of the vehicle (0.1 mL physiologic saline solution)15 minutes before surgery and on the four consecutive postoperative days. The experimental groups received subconjunctival injections of either 40 µg (group D) or 100 µg (group E) decorin dissolved in 0.1 mL vehicle solution 15 minutes before surgery and on the four postoperative days. Group F received only a preoperative injection of 100 µg decorin. Animals in group G received 100 µg decorin before surgery and on postoperative days 1, 3, and 7.
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20% difference in IOP, reflected as an IOP ratio of
0.8.
Histologic Evaluation
On postoperative day 14, the eyes were enucleated together with the conjunctiva to preserve the bleb. The globes were immediately fixed in 10% formaldehyde for at least 24 hours. Consequently, the eyes were examined, and a ring in the sagittal axis comprising the relevant area excised. Tissue samples were then dehydrated and embedded in paraffin, and 5-µm serial sections were cut, rehydrated, stained with hematoxylin and eosin and the Masson technique, and coverslipped.
Statistical Evaluation
Statistical analysis was performed to determine the differences in IOP between the control and experimental groups. A two-tailed Students t-test was performed, and significance was assumed if P < 0.05.
Photographs
Clinical photographs were produced with a digital camera (model DCR-TRV50E; Sony, Tokyo, Japan). Histologic specimens were examined and documented with a microscope (Axioskop; Carl Zeiss Meditec, Oberkochen, Germany) connected to a digital camera (model HC-300Z; Fujix, Tokyo, Japan) and the appropriate hard- and software (Image Access, ver. 3.2; Imaging Bildverarbeitung AG, Glattbrogge, Switzerland).
| Results |
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Wound healing was clinically observed as the loss of conjunctival transparency and thickening due to the deposition of fibrotic tissue (Fig. 2A) . In both control groups B and C, scarring of the conjunctiva was prominent. The subconjunctival fibrotic tissue covered and impaired the view of the scleral flap. No bleb formation was detectable on day 14 after surgery. In contrast, suppression of scarring maintained a translucent conjunctiva (Fig. 2B) . This situation was consistent in groups E and G, but less pronounced in groups D and F. No cystic bleb formation was observed in groups E and G. The filtering zone was diffusely elevated.
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The higher concentration (100 µg) of decorin seemed to yield better results without increasing the risk of side effects. Group E, which received the same regimen but a higher dose of decorin than in group D, showed mean ratios of 0.60 ± 0.02 on day 7 (P < 0.05), 0.59 ± 0.02 on day 10 (P < 0.001), and 0.58 ± 0.11 on day 14 (P < 0.001; Fig. 3A ). However, there was no significant difference between groups E and D.
To examine whether a single preoperative injection of 100 µg decorin would have an effect, a single-dose regimen was applied in group F (Fig. 3B) . On day 7, the mean value was 0.70 ± 0.15 (P < 0.05) with two eyes outside of the defined success limit (IOP ratio
0.8). On days 10 and 14, there was no statistically significant difference from control animals.
To cover the critical wound-healing phase, but reduce the number of injections, in group G, 100 µg of decorin was applied before surgery and on postoperative days 1, 3, and 7 (Fig. 3B) . This dose regimen could retain significantly low IOP-ratios over the time of evaluation. The mean ratios were 0.60 ± 0.1 on day 7 (P < 0.05), 0.58 ± 0.04 on day 10 (P < 0.001), and 0.66 ± 0.03 on day 14 (P < 0.001).
Histologic Appearance
All rabbits in groups B to G were killed on postoperative day 14, and the treated eyes were enucleated for histologic examination. The tissues were stained with hematoxylin and eosin to give an overall impression and with the Masson technique to determine the collagenous extracellular matrix (ECM) deposition.
Histologic analysis of the specimens was performed at the center of the sclerotomy site as indicated by the location of the iridectomy. Histologic profiles revealed massive subconjunctival scarring in the control groups (Fig. 4A) . The subepithelial connective tissue consisted of a dense collagenous connective tissue. The sclerotomy site was infiltrated by hypercellular fibrotic tissue (Fig. 4C) . Experimental groups, in contrast, showed only a mild fibrotic response (Fig. 4B) . The biomicroscopic impression of a translucent conjunctiva with no or mild ECM deposition was supported by the histologic examination. The conjunctival epithelium looked healthy, and there was only a mild deposition of collagen in the subconjunctival space (Fig. 4D) . The subepithelial connective tissue was loosely arranged and contained histologically clear spaces. Furthermore, the eyes did not reveal an intra- or extraocular inflammatory reaction. The corneal epithelium and endothelium, as well as the lens and the ciliary body did not show light-microscopically detectable signs of toxic effects.
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| Discussion |
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An anti-fibrotic effect of decorin has been demonstrated in experimental kidney,24 35 lung,36 cerebral,37 and muscular38 fibrosis. Ours is the first report of an antifibrotic effect of decorin in a rabbit model of filtration surgery.
Because of the aggressive wound-healing response in rabbits, this animal model is believed to be equivalent to high-risk eyes in humans, and surgical failure results within 1 week. The use of antifibrotic drugs, such as 5-fluouracil and mitomycin C, prolongs bleb survival. However, the effect is not permanent and, depending on drug concentration, it will subside within 2 weeks.18
Our experiments show that filtration surgery success can be prolonged when decorin is applied locally. As demonstrated in control group B, wound closure occurred and IOP increased within 1 week. This time until surgical failure was similar to that reported in previous studies. Group C demonstrates that the injection of the vehicle alone and the procedure of punctation and injection does not significantly affect the time of surgical failure.
Decorin was administered on day 0, approximately 15 minutes before surgery (groups DG). Further injections were administered on days 1, 2, 3, and 4 (groups D and E) or on days 1, 3, and 7 (group G). The rationale for this dose regimen was to achieve local availability of decorin at the critical time and to mimic clinical application that would be practicable.
In this study, multiple applications of 40-µg decorin (group D) showed a delayed increase of IOP and a decreased deposition of fibrotic tissue within the surgical area. In group E, 100 µg decorin was highly effective in retaining significantly reduced IOP R/L ratios. This was reflected in reduced scar tissue formation. The reduced fibrous response was observed biomicroscopically and supported by the histologic sections obtained at postsurgical day 14.
In a previous study, Cordeiro et al.14 demonstrated the effectiveness of a novel recombinant monoclonal neutralizing antibody to human TGF-ß2 on cultured conjunctival fibroblasts and in a rabbit model of glaucoma filtration surgery. These British colleagues used a modified filtration surgery technique that includes the insertion of a 22-gauge, 25-mm Venflon 2 (Ohmeda AB, Helsingborg, Sweden) intravenous cannula through a scleral tunnel into the anterior chamber. Using this technique, they maintained a patent channel through the sclera to maximize aqueous outflow. This seems, on the one hand, to allow a better bleb evaluation to define clinical success; on the other hand no significant changes in IOP were detected.14 In our study, we chose to use a surgical technique that is close to that used in our clinical practice. This procedure included the preparation of a scleral flap, partial sclerectomy with a trephine, and basal iridectomy with forceps. We described the appearance of the superior bulbar conjunctiva, but we did not quantify bleb survival. We defined clinical success as dependent on changes in IOP. In our experience,15 IOP measurements are less subjective and better quantifiable than bleb appearance and survival. Furthermore, we excluded interindividual, cyclic, and anesthesia-related variations by comparing the IOP between the experimental right eye and the left control eye. The difference in measured IOP was expressed as the R/L IOP ratio. Using this technique, a reduced IOP ratio was found in all animals at the third day after surgery (Fig. 3) . The aggressive scarring in this animal model, however, consistently leads to preoperative levels within 1 week.
The successful clinical and histologic anti-scarring effect of decorin supports the data found with the anti-TGF-ß2 antibody. We assumed in addition that decorin may be even more potent, because its inhibitory effect is not restricted to the TGF-ß2 isoform. Furthermore, it has been demonstrated recently that decorin has an inhibitory effect on platelet-derived growth factor (PDGF), a further major player in wound healing.39
This pilot study demonstrated that locally applied decorin improved glaucoma filtration surgery in an animal model of aggressive conjunctival scarring. Furthermore, subconjunctival decorin application appeared clinically safe and well tolerated within the experimental time. No signs of an inflammatory or toxic response were seen either biomicroscopically or histologically. Further studies are needed to examine the long-term effect and safety of perioperative subconjunctival decorin applications.
| Footnotes |
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Submitted for publication July 29, 2004; revised September 17, 2004; accepted October 7, 2004.
Disclosure: S. Grisanti, None; P. Szurman, None; M. Warga, None; R. Kaczmarek, None; F. Ziemssen, None; O. Tatar, None; K.U. Bartz-Schmidt, None
The publication costs of this article were defrayed in part by page charge payment. This article must therefore be marked "advertisement" in accordance with 18 U.S.C.
1734 solely to indicate this fact.
Corresponding author: Salvatore Grisanti, Department of Ophthalmology I, Eberhard-Karls University Tübingen, Schleichstrasse 12-15, 72076 Tübingen, Germany; salvatore.grisanti{at}med.uni-tuebingen.de.
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