A randomized phase II trial of interferon-alpha2b versus 5-fluorouracil after trabeculectomy

Anti-scarring effects of butaprost on human subconjunctival Tenon's fibroblasts

AIM

To investigate the toxicity of the E-prostanoid 2 (EP2) receptor agonist, butaprost against human subconjunctival (Tenon's capsule) fibroblasts, and to determine the underlying mechanism.

METHODS

We isolated Tenon's fibroblasts from the subconjunctival area of healthy subjects and evaluated the types of EP receptors expressed using quantitative real-time reverse transcription polymerase chain reaction (RT-PCR). The toxicity of butaprost against the fibroblasts was evaluated using methyl thiazolyl tetrazolium and lactic dehydrogenase assays. The inhibition of conjunctival fibroblast proliferation by butaprost was assessed by measuring α-actin levels. The underlying mechanism was assessed by measuring intracellular cyclic adenosine monophosphate (cAMP) levels. Intergroup differences were statistically analyzed using an independent t-test. Densitometry of the Western blot bands was performed using the Image J software.

RESULTS

Quantitative real-time RT-PCR revealed that the fibroblast EP2 receptor levels were higher than those of the other EP receptors. Butaprost did not show toxicity against Tenon's tissue, but inhibited conjunctival fibroblast proliferation by reducing collagen synthesis. EP2 receptor activation enhanced the cAMP cascade, which might be an important mechanism underlying this effect.

CONCLUSION

Butaprost effectively reduces the subconjunctival scarring response. Given the significance of wound healing modulation in blebs, butaprost's inhibitory effect on subconjunctival Tenon's fibroblasts may be beneficial in managing postoperative scarring in glaucoma surgery.

Modulation of wound healing in glaucoma surgery

Glaucoma is a neurodegenerative disease and is the second most important cause of irreversible blindness. Filtration surgery remains the most effective therapy to reduce intraocular pressure in glaucoma patients. The main determinant of long-term surgical success is the healing response. Excessive postoperative wound healing with subsequent fibrosis may lead to obstruction of the created channel which frequently results in early surgical failure and consequent progression of visual field loss. Preoperative use of antimitotics, such as mitomycin-C and 5-fluorouracyl, effectively improves surgery outcome. However, the use of these nonspecific antiproliferative agents can be associated with severe side effects. This review provides an overview of the most important efforts that have been made to explore novel, more specific, and safer agents to prevent glaucoma filtration failure and improve surgery outcome.

Interferon-alpha and interferon-gamma modulate Fas-mediated apoptosis in mitomycin-C-resistant human Tenon's fibroblasts

BACKGROUND

The aim of the study was to investigate, using a native mitomycin-C-resistant human Tenon's fibroblast cell line, the possibility that interferon-alpha and gamma could be used with Fas agonists as an alternative anti-fibrotic strategy to mitomycin-C in trabeculectomy.

METHODS

A clinically resistant and in vitro verified mitomycin-C-resistant human Tenon's fibroblast cell line was pretreated with interferon-alpha and interferon-gamma for 48 h before stimulation with an agonistic Fas antibody (CH11) for 2 days to induce cell death. Cell death assays were undertaken. Changes in apoptosis-related proteins were determined by flow cytometry and Western blot.

RESULTS

Pretreatment with interferon-alpha or interferon-gamma for 48 h increased Fas, Fas-associated protein with death domain and caspase-8 expression. Protein expression was further increased by combined exposure to interferon-alpha and gamma. Pretreatment with cytokines had no effect on Fas-L and Bcl-2. Interferon-alpha alone did not change the rate of induced cell death. A combination of interferon-alpha and gamma synergistically increased the sensitivity of mitomycin-C-resistant human Tenon's fibroblast cell line to induced cell death. An antagonistic anti-Fas antibody (ZB4) completely blocked induced cell death. Broad caspase inhibitors specific for caspases-8 and -3 reduced induced deaths in interferon pretreated mitomycin-C-resistant human Tenon's fibroblast cell line in a dose-dependent manner.

CONCLUSIONS

Interferon-alpha and interferon-gamma render mitomycin-C-resistant human Tenon's fibroblast cell line sensitive to Fas-mediated apoptosis. The mechanism involves increased death-inducing signalling complex formation by upregulation of Fas, Fas-associated protein with death domain and caspase-8 expression.

Modulation of wound healing during and after glaucoma surgery

Following all types of glaucoma filtration surgery (GFS), scarring still poses the major threat to long-term success. The healing and scarring determine the percentage of patients achieving low final intraocular pressures (IOPs) that are associated with virtually no glaucoma progression. The use of antifibrotic agents to inhibit scarring of trabeculectomy blebs is now a well-established clinical practice. Unfortunately, severe complications such as leakage, infection, hypotony, and endophthalmitis with complete loss of vision may occur. In addition, surgery still fails in some individuals despite maximal doses of current antifibrotics. Better therapeutic agents are needed. Many promising new agents are being evaluated clinically and in vitro. In this chapter, we will discuss our current understanding of the wound healing process after glaucoma surgery and promising new treatment modalities.

In vivo production of interferon beta by human Tenon's fibroblasts; a possible mediator for the development of chronic conjunctival inflammation

BACKGROUND

Chronic inflammation may develop from failure of the immune system to deactivate itself during resolution of the wound healing response, and is recognised as a major risk factor for trabeculectomy failure. Fibroblast/T cell interactions may contribute to aggressive scarring. Our previous research showed that in vitro human Tenon's fibroblast produced interferon beta was responsible for preventing T cell apoptosis, suggesting that this interaction could contribute to the development of chronic inflammation.

METHODS

Immunohistological techniques were used to investigate the in vivo components of this particular fibroblast/T cell interaction in conjunctival biopsies from glaucoma patients undergoing filtration surgery.

RESULTS

Fibroblast produced interferon beta and T lymphocytes were identified in human conjunctiva.

CONCLUSION

The components of fibroblast mediated prevention of T cell apoptosis were identified in vivo, suggesting that the development of this interaction is possible and that it may contribute to the development of chronic inflammation and excessive scarring.

A murine cell culture model for post-trabeculectomy anfibrotic treatment: Induction of apoptosis by Cyclosporin

PURPOSE

Experimental trials aimed at the research of selective antifibrotic agents are under development for the alternative treatment of glaucoma patients who are usually considered high-risk post-surgical individuals after trabeculectomy. Authors present here an in vitro model system for the treatment of post-trabeculectomy patients. The study is aimed at the evaluation of different drugs in a mouse fibroblast model.

METHODS

The antifibrotic activity of Cyclosporin A, Interferon 2alpha, 5-Fluorouracyl was investigated on 3T6 cells in culture. Cell viability and proliferation was assessed after drug treatment. Molecular analysis of DNA degradation was evaluated by means of radioactive labeling and gel electrophoresis.

RESULTS

The three drugs were shown to affect cell proliferation and viability in a differential fashion. However, only Cyclosporin A was able to control cell proliferation, inducing apoptosis. This phenomenon was reduced by supplementation of trolox, a compound known to inhibit programmed cell death. These results strongly suggest that this model system might be useful as a test of pharmacological functionality.

CONCLUSION

A rapid and efficient model system is described for the assessment of cell viability and proliferation after treatment with agents of potential pharmacological use. Cyclosporin A induces a significant apoptosis. This is important for the negative control of fibrotic degeneration in post-trabeculectomy that is required for successful surgery in glaucoma patients. Therefore, Cyclosporin A might become a clinically interesting drug for the antifibrotic treatment of post-trabeculectomy.

Modulation of wound healing after glaucoma surgery

The healing process after glaucoma filtration is the main determinant of surgical failure and, even more important, the final intraocular pressure. The ability to fully control wound healing may ultimately give us the ability to set the intraocular pressure in the low teens for all patients undergoing glaucoma filtration surgery. The authors review the changes in how to use antimetabolites to improve safety, and many of the exciting new areas of progress, including growth factor neutralization and future molecular therapies to control wound healing.

The role of the immune system in conjunctival wound healing after glaucoma surgery

The immune system has a fundamental role in the development and regulation of ocular healing, which plays an important role in the pathogenesis of most blinding diseases. This review discusses the mechanisms of normal wound healing, describing the animal and fetal wound healing models used to provide further insight into normal wound repair. In particular, conjunctival wound repair after glaucoma filtration surgery will be used to illustrate the contributions that the different components of the immune system make to the healing process. The potential role of macrophages, the possible regulatory effect of lymphocytes, and the important role of growth factors and cytokines in the wound healing reaction are discussed. The significance of the immune system in the pathogenesis of aggressive conjunctival scarring is addressed, particularly assessing the predisposing factors, including drugs, age, and ethnicity. The rationale behind the pharmacological agents currently used to modulate the wound healing response and the effects these drugs have on the function of the immune system are described. Finally, potential new therapeutic approaches to regulating the wound healing response are reported.

Modulating conjunctival wound healing

Advances in molecular and cell biology have led to an expansion in our knowledge and understanding of the processes involved in wound healing. We review existing and potential therapies modulating the conjunctival scarring response, with particular reference to glaucoma filtration surgery. We discuss how the refinement of present antimetabolite regimens can minimise complications and improve surgical results, and advocate their use in carefully selected patient groups. Perhaps the most promising approach is targeting biological molecules. Hence, use of fully human neutralising monoclonal antibodies to the growth factor TGF beta has potential as a useful strategy for modifying conjunctival scarring. Combination therapies may also afford an improved therapeutic index. It is hoped that future therapies can offer safer, more specific, focal and titratable treatment, with far-reaching clinical applications.

Wound healing modulation after glaucoma surgery

Recent developments in molecular and cell biology have made a major impact on our understanding of the wound healing process and its modification. In this article, the spectrum of therapies that are either currently available or have potential application as modulators of the scarring response following glaucoma surgery are reviewed. Refinement of existing antimetabolite regimens can improve surgical results, especially in carefully selected patient groups. However, the most promising new approach appears to be using molecular-based therapies, such as fully human neutralizing monoclonal antibodies, designed to target specific molecules in the scarring response. Such strategies ultimately offer the potential of safer, more specific, focal, and titratable treatment, with far-reaching clinical applications.