ACTIVATION AND SUPPRESSION OF FIBROBLAST FUNCTION

3 3 3 2 P. T. KHAW1.2, , N. L. OCCLESTON1, , G. SCHULTZ2, , 1. GRIERSON1A, M. B. SHERWOOD and G. LARKINl London

SUMMARY optic nerve head. Glaucoma is not a single disease process The fibroblast is the central player in the wound repair but rather a large group of diseases, which have in common and scarring processes that occur in the anterior segment damage to the optic nerve head. This group of diseases will of the eye. Glaucoma filtration surgery is the ultimate soon be the second commonest cause of blindness in the example of the importance of the wound healing process, world behind cataracts, affecting people in both developed as this process is the major determinant of the success of and developing countries.l.2 Unlike cataracts, the blindness this procedure. We highlight the role of the fibroblast, from glaucoma is essentially irreversible. Although many and discuss some of the growth factors stimulating fibro­ theories for the pathogenesis of optic nerve damage have blast proliferation, migration and extracellular matrix been postulated, the major risk factor for glaucomatous production in the wound environment. We also review optic nerve damage is the level of intraocular pressure. The current methods of suppressing fibroblast proliferation, higher the intraocular pressure, the greater the risk of optic the new concepts that have arisen from laboratory stud­ nerve damage.3,4 Most treatment is aimed at reducing the ies, and future directions of investigation and treatment. intraocular pressure. There are three main categories of treatment: medicine, The processes involved in tissue repair play a critical role laser or surgery. In recent years evidence has been accumu­ in either the pathogenesis or failure of treatment of most of lating that surgery is superior to either laser or medical the major blinding or visually disabling conditions in the treatment in lowering the intraocularpressure5 and preserv­ world today. The biological processes that result in scar­ ing vision.6-9 In addition, successful surgery results in a bet­ ring account for a great deal of visual morbidity. In this ter quality of life for patients compared with medical review we use glaucoma filtration surgery as an example treatment,IO and the use of topical medication (eyedrops) of the importance of scarring, as a model of the scarring I I increases the chance of subsequent surgical failure. process after ocular surgery, and also highlight the role of Furthermore, in many developing countries of the world, the fibroblast, the factors that may activate the fibroblast, surgery is the only practical treatment to prevent blindness and the effects of methods used to suppress fibroblast from glaucoma. function. Glaucoma filtration surgery involves the creation of a GLAUCOMA FILTRATION SURGERY: AN new drainage channel for the aqueous humour to flowout of EXAMPLE OF THE IMPORTANCE OF THE the eye and thus lower intraocular pressure. The common­ est form of the procedure 12 involves making an incision in SCARRING PROCESS the conjunctiva, dissecting open the subconjunctival space The glaucomas are a group of disorders characterised by and making a trapdoor incision in the sclera up to the junc­ optic nerve head damage, visual field loss and an intra­ tion between the cornea and the sclera. The eye is entered ocular pressure sufficientlyraised to affect function of the and a block of corneoscleral tissue removed to create a new From: International Collaborative Wound Research Group: I Institute channel for aqueous outflow, and the trapdoor sutured of OphthalmologylMoorfieldsEye Hospital, London, UK; 'Institute for down to create a valve mechanism. The conjunctival inci­ Wound Research, University of Florida, USA; 3Phoenix Department Plastic Surgery, University College, London, UK: "Department of sion is then closed and the aqueous allowed to flow out Ophthalmology, University of Liverpool, UK. under the conjunctiva. The aqueous may then flow away Correspondence to: Mr Peng T. Khaw, MRCP, FRCS, FRCOphth, subconjunctivally, through aqueous veins, through lym­ Consultant Ophthalmic Surgeon, Glaucoma Unit and Wound Healing Group, Moorfields Eye Hospital and Institute of Ophthalmology, City phatics channels or transconjunctivally.13 Road, London ECIV 2PD, UK. The successful lowering of intraocular pressure afterfil-

Eye (1994) 8,188-195 © 1994 Royal College of Ophthalmologists FIBROBLAST FUNCTION 189 tering surgery relies heavily on the nature of the healing degree of blood-aqueous barrier breakdown occurS/I-33 response following the surgery. It is variations in this heal­ bringing in serum factors to the wound site. ing response that result in the majority of failed filtering Polymorphonuclear cells move into the wound area fol­ procedures. Several risk factors may increase the chance of lowed by lymphocytes and macrophages. Fibroblasts then filtrationsurgery failing and these are shown in Table 1. The begin to migrate towards sites of damage. As they migrate reasons for the increased scarring response in patients with they probably cause wound contraction. The tractional these risk factors are still unclear. Furthermore, just as forces exerted by moving fibroblasts have been elegantly important as absolute failure is suboptimal lowering of the demonstrated by Harris et at. 34 who seeded fibroblastsonto intraocular pressure. There is evidence that the greater pres­ ultrathin polymerised silicone. We have been using this sure lowering associated with surgery is associated with a model to investigate fibroblast-mediated wound contrac­ better visual prognosis.9 The healing response is the major tion; the forces generated by the moving fibroblasts are determinant of the finalintraocular pressure. In terms of the clearly seen in Fig. 1. The fibroblastsalso begin to prolife­ entire glaucoma population undergoing surgery, this is rate, which is necessary to generate sufficient numbers of probably a much more important problem epidemiologi­ cells to carry out the various wound-healing processes in a cally than the far smaller but highly visible group that com­ relatively short time. This process peaks within the first 2 pletely fail surgery. Thus the healing response is the single weeks after experimental glaucoma filtration surgery,3S-37 most important modifiable factor determining outcome in which is similar to cutaneous wounding. every patient undergoing glaucoma filtrationsurgery. Fibroblasts secrete fibronectin,glycosaminoglycans and

Table II. Sequence of events in wound healing and potential areas of CELLULAR EVENTS AFTER GLAUCOMA modification after glaucoma filtering surgery (simplified: events and FILTRATIONSURGERY AND THE ROLE OF agents have overlapping time duration and action) THE FIBROBLAST Event Possible areas of modulation The sequence of events following glaucoma filtering sur­ Conjunctival/episcleral/scleral Minimal trauma gery can be illustrated in a simplified diagrammatic form incisions Less invasive surgical techniques (Table II), although some of the events obviously occur ! concurrently. When incisions are made in the conjunctiva Damage to connective tissue Haemostasis Release of plasma proteins and Agents preventing/ and sclera, connective tissue and blood vessels are dam­ blood removing fibrin (e.g. heparin, aged. This results in the release of blood cells and plasma Activation of clotting and com­ tissue plasminogen activator) proteins into the damaged site. The clotting system is acti­ plement Antagonists to growth factor Fibrinlfibronectinlblood cell clot production. growth factor vated and clot forms around the damaged areas. This is Release of growth factors from activation (e.g. antisense similar to the events that occur after cutaneous or other blood oligonucleotides). antibodies to wounding. 1 growth factors or receptors However, the glaucoma filtration surgical site differs in Aqueous released from eye Blood�aqueous barrier stabilising one fundamental aspect: it is bathed by aqueous humour Breakdown of blood�aqueous agents (e.g. non-steroidal anti­ emerging from the eye through the newly created fistula. barrier inflammatory agents) Release of growth factors into Antagonists to growth factors This aqueous humour and its contents can have very signifi­ aqueous cant effects on the healing response afterglaucoma surgery. Aqueous begins to flow through There have been suggestions that the aqueous contains an wound ! inhibitory factor or factors,27,28 and aqueous clearly modu­ Migration and proliferation of Anti-inflammatory agents (e.g. lates the wound as dissected conjunctiva normally scars polymorphonuclear neutrophil steroids) down rapidly to the episclera without aqueous. However, cells, macrophages and Antiproliferative agents (e.g. lymphocytes S-fluorouracil) aqueous also has stimulatory effects on fibroblasts in ! vitro29•30 and in vivo. A particularly good example is the Migration and proliferation of Antiproliferative agents aggressive scarring seen after filtration surgery in patients fibroblasts Anticontraction agents (e.g. Wound contraction taxo!) with new vessel formation within the eye. In this situation ! the aqueous humour, which is presumably full of stimulat­ Fibroblast synthesis of Anticross-linking agents (e.g. ing factors, invariably induces rapid scarring and sub­ tropocollagen. beta-aminopropionitrile) glycosaminoglycans and sequent surgical failure. Even in a relatively undiseased eye fibronectin (e.g. cataract extraction), when the eye is entered some Collagen cross-linking and modification Table I. Risk factors for failure of glaucoma filtration surgery 1 Topical medications> I year1L14,15 Blood vessel endothelial migra­ Inhibitors of angiogenesis Age <40 yearsl6-20 tion and proliferation Afro-Caribbean21-2" ! Previous failed filter" Continued collagen synthesis Previous cataract surgery" Capillary resorption and Uveitis26 disappearance of fibroblasts 6 Anterior segment neovascularisation 2 t AphakiaJpseudophakia" Fibrous subconjunctival scar 190 P. T. KHAW ET AL.

which is the central cell of the scarring process. Filtration surgery most commonly fails because of the build up of extracellular matrix, in particular collagen which obstructs the flowof aqueous. Without the fibroblastcell this failure would not occur.

ACTIVATION AND STIMULATION OF THE FIBROBLAST Normally, the fibroblastexists within the subconjunctival connective tissue as a quiescent undifferentiated mesen­ chymal cell, the fibrocyte.This cell is found in low numbers throughout connective tissue. The fibrocyteconverts to the active fibroblastcapable of carrying out the various cellular functions responsible for wound healing when stimulated Fig. 1. Human Tenon's capsule fibroblasts seeded onto poly­ by various factors in the environment. For instance, factors merised silicone sheets. As the fibroblasts move and migrate they create marked surface tractional forces. which are known to stimulate fibroblast migration are the complement component C5a,41 growth factors such as tropocollagen which is then enzymatically cross-linked to platelet-derived growth factor, transforming growth factor form collagen. Collagen is a major component of the wound and fibroblast growth factor,42 elastin and collagen frag­ matrix and is a prominent feature of experimental filtering ments,43,44Ieukotriene, and fibronectin.45 These factors are surgery failure in the rabbit and monkey.36,38 Many fibro­ derived from damaged tissue, blood, inflammatory cells blasts in the failing blebs of rabbits have cytoplasm rich in such as macrophages, lymphocytes and macrophages, and endoplasmic reticulum, with some distended cisternae. from the fibroblaststhemselves. In the aqueous itself there This appearance is consistent with an actively metabolising are factors known to stimulate fibroblasts, and these are cell undergoing transcription.36 Collagen accumulation is listed in Table III. The relative roles of these growth factors also a prominent feature of failing blebs in man.39 in healing after wounding of the anterior segment of the eye This connective tissue is then remodelled continuously are unclear. for several months40 with continued synthesis and break­ We previously investigated the role of several growth down of the extracellular matrix. Eventually most of the factors in the migration of corneal fibroblasts46 and have active cellular processes cease and the finalresult is subcon­ more recently studied the effects of different concentra­ junctival scar. Successful filteringsurgery is usually asso­ tions (10-7 to 10-14 mM) of various growth factors including ciated with a subconjunctival accumulation of aqueous epidermal growth factor (EGF), basic fibroblast growth humour, or a 'bleb' (Fig. 2). Failed filtration surgery is factor (bFGF), transforming growth factor beta-l associated with a dense scar in the subconjunctival space (TGF-�l) and insulin-like growth factor 1 (IGF-I) on the which closes this potential space and prevents aqueous migration, collagen synthesis and proliferation of human flow. It is obstruction by scarring at the episcleral levels Tenon's capsule fibroblasts. We found that all four growth rather than the fistulaitself which is the main reason for fail­ factors stimulated proliferation, migration and collagen ure. The process of healing and the scarring response can be production to some degree, but that TGF-�l stimulated modulated at various points in the process, and these are proliferation at much lower concentrations than the other represented in Table II. However, most of the effortsto sup­ growth factors. In addition, TGF-�l also stimulated much press scarring have concentrated on the fibroblast cell, more collagen production than EGF and bFGF; it is of interest, though, that IGF-I also stimulated the same amount of collagen production as TGF-� 1, albeit at a higher concentration. These results suggest that targeting specific growth factors, in particular the TGF-� family, may be a reasonable approach to preventing post-operative scarring in the eye. There is already evidence that modulating the profileof the TGF-� family aftercutaneous wounding may reduce scarring.47

Table III. Some stimulatory factors in the aqueous humour

Fibroblast growth factor Epidermal growth factor" Transforming growth factor beta-l and beta-2 Insulin-like growth factor I Fibronectin Transferrin Fig. 2. A drainage bleb after glaucoma ,filtration surgery: Interleukin 6 collection of aqueous humour draining out of the eye under the conjunctiva. The edges of the bleb are marked with arrows. 'Controversial. FIBROBLAST FUNCTION 19 1

Table IV. Examples of some agents used to modulate ocular fibroblast mainly on the premise that if there are inadequate numbers function (some have more than one action) of cells, significantscarring cannot occur. However, it must Anticytoskeletal be borne in mind that these agents clearly have effects on Colchicine other aspects of fibroblast function. Cytochalasin b Blumenkranz and colleagues55.56 established that various Taxol Nocodazole antiproliferative drugs, in particular 5-fluorouracil, Vincristine inhibited the proliferation of fibroblastsduring a period of Vinblastine continuous drug exposure in cell culture and prevented epi­ Antiproliferatives retinal scarring in the eye in an animal model. Stimulated by Radiation this initial research, a regimen involving subconjunctival Doxorubicin Bleomycin injections of 5-fluorouracilwas developed at Miami culmi­ Chlorambucil nating in the multicentre 5-fluorouracil filtering surgery Cytosine arabinoside trial.25 Many studies have also been carried out investigat­ 5-Fluorodeoxyuridine 5-Fluorouracil ing the effects of 5-fluorouraciland many other antiprolife­ Methotrexate rative agents on ocular fibroblastsin culture in an attempt to Mitomycin C find an optimal agent,57-M and also to develop an optimal Gamma interferon Anti-transferrin receptor monoclonal antibody conjugated to a delivery system that does not require multiple injec­ cellular poison, ricin tions.49,65-7o However, Chen and colleagues71.72 had been Immunosuppressiveslanti-inflammatories using single applications of another anti-proliferative Prednisolone agent, mitomycin-C, for more than a decade, initially Dexamethasone Triamcinolone largely unnoticed. The use of this regimen has seen an expo­ Indomethacin nential increase in popularity over the last few years Meclofenamate sodium because of the ease of application and effectiveness. Cyclosporin Diphenhydramine One of the reasons for the initial reluctance to use Chen's regimen was the lack of knowledge as to how a single appli­ cation of these agents could suppress fibroblast prolifer­ MODULATION/SUPPRESSION OF ation adequately over the period of several weeks, during FIBROBLAST FUNCTION the period of maximal fibroblast proliferation. Our group A great deal of research has been carried out on agents has shown that several anti proliferative agents have long­ which directly or indirectly modulate various aspects of term effects on the proliferation of ocular fibroblasts,even fibroblastfunction (Table IV). Attempts have been made to when the time of exposure is as short as 5 minutes.73.74 Given target specific cell functions such as migration. Examples the appropriate concentration and agent, effective suppres­ are colchicine, cytochalasin B and particularly taxol (which sion of proliferation can be achieved for periods of up to 36 all affect the cytoskeleton of the cell), which were all shown days without significantcell death.73,75 To our surprise, this to inhibit the migration of fibroblasts to rabbit aqueous long-term suppression also occurred with5-fluorouracil,as humour.48 Taxol has been shown to prolong survival of fil­ the drug's inhibitory action on DNA synthesis through thy­ tration surgery in an aggressive model of filtration sur­ midylate synthetase should have been rapidly reversible. gery.49 Another example is the use of lathyrogenic agents However, 5-fluorouracil, has, like all other drugs, second­ such as beta-aminopropionitrile, which prevents collage? ary actions including interference with RNA synthesis, cross-linking by inhibiting the enzyme lysyl oxidase.oo and these may explain the longer-term actions. There is experimental and clinical evidence that this may We have subsequently shown that this long-term sup­ work.51-53 However, many of these 'specific' agents have pression of proliferation occurs in an in vivo experimental effects on other fibroblastfunctions: for instance taxol also model of glaucoma filtration surgery and appears to be inhibits cell proliferation and BAPN may also have anti­ titratable in terms of length of action.76,77 It is also focal in inflammatory effects.54 Most of the work aimed at inhibit­ . that only the fibroblastsIII the treated areas are aff ected . 7X,79 ing scarring after glaucoma filtration surgery has concen­ The fact that this suppression of fibroblast proliferation is trated on the inhibition of proliferation of ocular fibroblasts, focal is very important clinically, and the theoretical impli­ Table V. Theoretical implications of the concept of long-term, titrat­ cations are shown in Table V. Fibroblasts are not derived able, focal tissue suppression of fibroblast function from the blood as was previously thought, but are derived Simultaneous corneal surgery without inhibition of healing from a local population of fibrocytes. Therefore recovery of Titration of the final intraocular pressure by changing agents, local tissue healing due to fibroblasts can only occur if the concentration and area treated local tissue fibroblastsrecover from the focal treatment or if Creation of more diffuse thicker blebs (theoretically safer) by changing agents, concentration and area treated there is migration of fibroblastsinto the area. Positioning of thin drainage areas in the fornix away from vulnerable However, just as important as the effect on the cells areas such as limbus themselves is the length and degree of stimulation present Preoperative use of these agents may be possible in the aqueous and the wound area. This stimulation can Appropriate treatment to maximise anti-scarring effect and minimise modify the overall profile of healing despite fibroblast complications if individual healing responses are better understood modulation with the same treatment. A simplifiedmodel of 192 P. T. KHAW ET AL.

Long term suppression of C: "Persistent Response" fibroblast function after e.g. Neovascular Glaucoma a single application of mitomycin-c 0.4 mg/ml

B: "Exaggerated Response" e.g. Chronic Topical Medications "Excessive healing" line

"Excessive healing" line A: "Normal Response"

B: "Exaggerated Response"

A: "Normal Response"

TIME AFTER INJURY TIME AFTER INJURY (a) (c)

Fig. 3. (a) Different healing profiles. The 'normal' healing re5ponse(A: e.g. elderly Caucasian patient without previous top­ ical medications) peaks then rapidly plateaus, possibly with some fall back to baseline as aqueous under the conjunctiva is associ­ Temporary suppression of ated with some bleb thinning. This occurs without crossing above fibroblast function after an imaginary 'excessive healing' line. Neither does the healing fall below another imaginary 'inadequate healing' line, below a single application of which there may be complications such as hypotony. The 'exag­ 5-fluorouracil 25 mg/ml gerated' healing response (B: e.g. a patient who has received chronic topical medications) starts higher initially and reaches a C: "Persistent Response" higher peak compared with nonnal. The 'persistent' response (C: e.g. a patient with neovascular glaucoma and constant stimu­ "Excessive healing" line lation from the aqueous) rises to a high peak response after sur­ B: "Exaggerated Response" gery that continues for a very prolonged period. (b) Postulated effect of a single 5 minute application of a shorter-acting agent A: "Normal Response" such as 5-jiuorouracil. This causes temporary suppression (weeks) and this is adequate for a 'normal' and an 'exaggerated' re5ponse, but not for higher-risk patients with a 'persistent' response who then cross the 'excessive healing' line and fail sur­ gery. (c) Postulated effectof a single application of mitomycin-C. This suppresses the 'persistent' response but pushes a 'normal' response below the 'inadequate healing' line, and the 'exag­ TIME AFTER INJURY gerated'response to the borderline, potentially resulting in hypo­ (b) tony and other complications due to inadequate healing. this concept is shown in Fig. 3. Essentially, this model We have been looking at other aspects of fibroblastfunc­ represents three different profiles of healing, combined tion following suppression of proliferation. Another vital with a theoretical 'excessive healing' threshold line, which function of the fibroblast is its ability to contract extracel­ if crossed results in surgical failure. If excessive modula­ lular matrix. We have been using type I collagen gels popu­ tion is achieved, a theoretical 'inadequate healing' line is lated with ocular fibroblasts. The fibroblasts rapidly crossed and complications due to poor healing occur. The contract these collagen gels when stimulated with serum. theoretical effects of a shorter-term inhibition (5-fluoroura­ Five-minute exposures to 5-fluorouraciland mitomycin-C cil) and a longer-term inhibition (mitomycin-C) on these also inhibit the contraction of these gels. It is of particular different healing profilesis shown. The inhibitory effect of interest that the effects of treatment are very different mitomycin-C has been placed below the 'inadequate heal­ depending on the state of cellular activation of the fibroblast ing' line as we now have good in vivo73 and in vitro80 evi­ in the gel before treatment. A 'primed' cell may respond to dence that part of the effect of mitomycin-C at this treatment very differently from a 'quiescent' cell, further concentration is due to actual cytotoxicity, while the emphasising the importance of the environment of the tis­ remaining cells are growth arrested. Therefore, although sues in individual patients before and after wounding. Top­ we know we can adequately suppress fibroblast prolifer­ ical medications, the commonest form of treatment for ation in a relatively titratable manner with practical single­ glaucoma, have a significant effect on conjunctival cellu­ application treatments, we still need to know more about larity,81 amount of shrinkage82 and the response to surgery. II the individual healing responses, and what functions the On a more molecular level, we have found that the 'sup­ suppressed fibroblast is able to carry out under these pressed' growth-arrested fibroblasts are still able to conditions. respond to stimulatory factors found in the wound environ- FIBROBLAST FUNCTION 193

ever, what this pilot experiment confirmsis that the effects Untreated Cells Growth arrested cells 2 days 5·FU 100 I'glmi of local suppression of fibroblasts can be significantly

Collagen la2 altered by changes in the wound environment. In summary, we now have a variety of effective methods ,. ·5.2 Kb· to suppress fibroblast function. In particular, the single I exposures to anti proliferative agents are at present the most 3 4 practical method of achieving fibroblast suppression after Lysyl Oxidase glaucoma filtration surgery. From basic research we now understand a great deal more about how these treatments tlit ·4.3 Kb· work in vitro and in vivo. However, we have also shown that 4 the state of activation of the cell, and the stimulatory factors activating the cell, can have profound effects on the healing Transforming Growth FaCl0c-B 1 response mediated by the' suppressed' cells and tissues as a

. 2.5 Kb . whole. A deeper understanding of the basic cellular and •• molecular biology of the healing process, variations in dif­ 4 6 ferent individuals and circumstances and the effects of Cu Zn Superoxide Dismutase Loading control modulating agents on the fibroblastin particular are essen­ tiaL With this knowledge, we may then be able to achieve

·0.6 Kb· totally safe but effective control of the scarringprocess, not III I just in the eye but in the whole human body. 3 4 6

Lanes 1 2 3 4 5 6 DMEM DMEM DMEM DMEM DMEM DMEM No TGF·nl TGf·nl No TGf·nl TGF·nl TGF·nl 5 pM 500 pM TGF·nl 5 pM 500 pM

Fig. 4. Effects o.ftransforming growth factor beta-I (TGF-PI) stimulation on RNA levels of collagen, lysyl oxidase and TGF-pI in normal and 'growth-arrested' ocular fibroblasts. RNA levels of collagen Iu2, lysyl oxidase and TGF-pi all showed an increase when treated with 500 pmol TGF-pl. The cells growth arrested with 5-fiuorouracil also showed relatively normal RNA levels of collagen and TGF-pI, with an increase when stimulated with TGF-pl. However, the levels of lysyl oxi­ dase were markedly reduced, although there was still a response to stimulation with TGF-pl. NB. lane 4 underloaded. (a) ment such as TGF-�L This is illustrated in Fig. 4. We found that Tenon's capsule fibroblasts show an increase in RNA levels of collagen I(X2 and TGF-�l when exposed to increasing concentrations of TGF-�L This has been well described in other fibroblasts. It is of interest too that the levels of lysyl oxidase are also upregulated by TGF-�L After the cells have been growth arrested with 5-fluoroura­ cil, they are still able to respond to TGF-�l by upregulating levels of collagen I(X2and TGF-� 1 with slightly attenuated but nonetheless similar responses to untreated cells. It is interesting that there is a differential effect on the RNA levels of lysyl oxidase which were much lower, although there was still an increase in RNA levels with higher con­ centrations of TGF-�l. So suppressed cells, although growth arrested, are still able to respond to exogenous (b) stimulation at the level of transcription. On the basis of these studies we have performed pilot Fig. 5. Effectof exogenous growth factor (TGF-PI) on the area growth arrested with a single 5 minute application of mitomy­ studies in vitro on drainage blebs induced by mitomycin-Co cin-C. (a) Rabbit eye 40 days after treatment with a 5 minute When the blebs are injected with growth factors including exposure to mitomycin-C during experimental filtrationsurgery. TGF-�l a healing response is generated which begins to Injection of control carrier at day 30. The bleb is still enlarged reverse the effects of the mitomycin-C (Fig. 5). Thick scar and draining. (b) Rabbit eye 40 days after treatment with a 5 tissue develops surrounding the bleb and the bleb begins to minute exposure to mitomycin-C before glaucoma filtrationsur­ gery. injected with TGF-pl/carrier into bleb. The bleb has con­ opacify and shrink compared with the effect of a control tracted from the periphery inwards. Thick subconjunctival scar injection of carrier only. We are currently investigating the tissue is present in surrounding tissue(s) including the injection cellular and molecular mechanism of this scarring. How- track (dotted line with arrow). 194 P. T. KHAW ET AL.

These studies were funded in part by the Wellcome Trust, the 23. Iliff CEo Surgical control of glaucoma in the Negro. Am J Oxford Congress Scholarship, the TFC Frost Charitable Trust, OphthalmoI1944;27:731-8. Moorfields, LORS and NIH grant EY 05587. We thank Dr 24. Merritt Je. Filtering procedures in American blacks. Oph­ Thomas Yang and Dr Harry Nick for the cDNA probes for Iy syl thalmic Surg 1980;11 :91--4. oxidase and superoxide dismutase. We also thank Ms Vicki Scott 25. The fluorouracil filtering surgery study group. Fluorouracil for her expert assistance with the preparation of this paper and the filtering surgery study: one-year follow-up. Am J Ophthal­ illustrations. mol 1989;108:625-35. 26. Heuer DK, Parrish RK II, Gressel MG, Hodapp E, Desjardins Key words: Antiproliferative agents, Fibroblast, Growth factors, RNA, DC, Skuta GL, et al. 5-Fluorouracil and glaucoma filtering Scarring, Wound healing. surgery. III. Intermediate follow-up of a pilot study. 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