Cellular photoablation to control postoperative fibrosis in filtration surgery: in vitro studies

Safety and efficacy of photodynamic therapy using BCECF-AM compared to mitomycin C in controlling post-operative fibrosis in a rabbit model of subscleral trabeculectomy

AIM

To evaluate the safety and efficacy of cellular photoablation using BCECF-AM [2', 7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, acetoxymethyl ester mixed isomers] as a method to control postoperative fibrosis in subscleral trabeculectomy (SST) compared to mitomycin C (MMC) in a rabbit model.

METHODS

A comparative prospective case-control animal study was conducted. Fourteen rabbits were subjected to SST with intraoperative use of wound modulating agents (MMC or BCECF-AM) of the right eye (study groups I and II respectively) and SST without use of intraoperative wound modulating agents for the left eye (control group II). Two rabbits 4 eyes were considered as control group I with no surgical intervention. BCECF-AM was injected subconjunctivally 30min before surgery followed by intraoperative illumination with diffuse blue light for 10min. Antifibrotic efficacy was established by clinical response and histological examination. Clinical response was assessed by measuring intraocular pressure (IOP) at day 1, 3, 5, 7, 14, 21 postoperatively. Success was defined by >20.0% reduction in IOP from the preoperative values without anti-glaucoma medications.

RESULTS

The mean percentage of reduction was 35.0% in the study group I with only one eye (14.3%) had 12.5% reduction. The mean percentage of reduction was 28.0 % in the study group II with two eyes (28.6%) in study group II had 14.2% reduction each. Regarding the control group II, the mean percentage of reduction was 14.3 % with 64.3% eyes had <20.0% reduction. There was a highly statistically significant difference between each of the study groups (right eyes) and the corresponding control group II (left eyes) as regards the mean postoperative IOP values started from day 5 in both study groups and this highly significant difference remained so till the end of the follow up period. Histologically, MMC treated blebs showed thinning of conjunctival epithelium with marked reduction of the goblet cells relative to control. Marked sub-epithelial edema was seen along with variable collagen dispersion. Mild cellularity was noted in sub-epithelial tissue. BCECF-AM treated blebs showed normal conjunctival epithelial thickness with abundant goblet cells. Mild sub-epithelial edema was noted along with moderate collagen dispersion. No histological abnormality was noted in the ciliary body or the cornea in any of the studied groups.

CONCLUSION

Cellular photoablation using BCECF-AM is a safe and effective wound modulating agent to control postoperative fibrosis in trabeculectomy. However MMC considered as a more potent adjuvant to trabeculectomy than BCECF-AM in promoting IOP reduction.

Wound modulation after filtration surgery

Filtration surgery is the standard invasive procedure for the management of intraocular pressure in advanced glaucoma. The key to a successful outcome is to modulate the normal wound healing cascade that leads to closure of the newly created aqueous outflow pathway. Antifibrotic agents such as mitomycin C and 5-fluorouracil have been increasingly used to modulate the wound healing process and increase surgical success. Although these agents have proven efficacy, they also increase the risk of complications. Efforts have centered on the identification of novel agents and techniques that can influence wound modulation without these complications. We detail new agents and methods under investigation to control wound healing after filtration surgery.

Comparative study between trabeculectomy with photodynamic therapy (BCECF-AM) and trabeculectomy with antimetabolite (MMC) in the treatment of primary open angle glaucoma

Background

Various methods have been investigated to avoid postoperative scarring of the filtering bleb in modern glaucoma surgery. Most deal with the application of antimetabolic drugs such as mitomycin C (MMC). 2′,7′-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, acetoxymethyl ester (BCECF-AM) is a locally acting intracellular photosensitizer which could control and decrease postoperative fibrosis at the trabeculectomy site.

Purpose

To compare the effect of photodynamic therapy in combination with trabeculectomy to the effect of MMC combined with the same procedure in controlling postoperative intraocular pressure (IOP) in patients with medically uncontrolled primary open angle glaucoma (1ry OAG).

Methods

A randomized controlled clinical trial was conducted on 76 eyes of 76 patients divided into three groups undergoing trabeculectomy, trabeculectomy with BCECF-AM (group A), trabeculectomy with MMC (group B), and trabeculectomy only as a control group (group C). Patients were reviewed postoperatively for clinical evaluation and photo documentation of the blebs with a fundus camera and ultrasonic biomicroscopy (UBM). The desirable effect of the adjunctive material was evaluated according to the clinical efficacy, tolerability, and safety by comparison with the control group.

Setting

Benha University Hospital, Benha, Egypt.

Results

After a mean follow-up of 24 months, all procedures succeeded in lowering IOP. The cumulative probability of complete success at the 24 month follow-up was 91% for group B, compared to 82% and 81.5% for group A and group C, respectively. The percentage of complete success was highest for group B, second highest for group A, and lowest for group C over the follow-up period; however, these differences were not statistically significant (P > 0.05). Regarding the bleb morphology and UBM reflectivity, the differences were not statistically significant (P > 0.05). The mean bleb height and breadth were larger in groups A and B in comparison to group C over the study period. The mean aqueous drainage route was similar in groups A and C, but less than in group B at 3 and 12 months postoperatively. Complications were generally mild and less marked in group A and C than group B.

Conclusion

Cellular photoablation using BCECF-AM seems to be a feasible new method to use in combination with glaucoma filtration surgery. Although MMC might be considered a more potent adjunctive to trabeculectomy in promoting IOP reduction, photodynamic therapy carries relatively less risk of adverse effects and complications. Cellular photoablation using BCECF-AM could be considered efficient, tolerable and relatively safer in managing patients with 1ry OAG. Further studies are necessary to determine the safety and the reliability of this therapy.

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.

Synergistic effects of combined cytotoxic and apoptosis-inducing drugs on Tenon's capsule fibroblasts in vitro and in vivo

BACKGROUND

Highly toxic antimetabolites have gained access to routine clinical use to modulate and reduce the amount of postoperative scarring following glaucomatous filtering procedures. It could be speculated that by combining two different antiproliferative substances with different mechanisms of action total amounts of the substances could be decreased and side effects reduced.

METHODS

Twenty-two substances were tested that had antiproliferative effects by acting cytotoxically, inhibiting growth factors, or inducing apoptosis. With combinations of each two substances, cell culture experiments using 3T3 and human Tenon's capsule fibroblasts were performed evaluating cell toxicity, proliferation and migration, the extent of free radicals, and the amount of apoptosis (TUNEL, electron microscopy). The five most potent combinations were used in an animal experiment with rabbits performing filtering procedures. The extent of episcleral scarring was evaluated by histopathology.

RESULTS

The results of the various assays revealed consistently strong effects in 5 of the 462 combinations. Of these five combinations, two were highly effective in the rabbit model. Substances with strong effects when applied in combination included staurosporine, mitomycin, and CD95L.

CONCLUSIONS

We found synergistic effects in assays that evaluated different aspects of cell function. The amount of scarring in an animal experiment was inhibited to a level comparable with a high single dose of mitomycin. Combination therapy of two antiproliferative acting substances may be a promising concept.

Photodynamic treatment in a rabbit model of glaucoma surgery

PURPOSE

To evaluate the safety and efficacy of postoperative verteporfin photodynamic treatment as an adjunct to glaucoma experimental filtration surgery in rabbits.

METHODS

Dutch belted (n = 15) rabbits underwent full thickness sclerectomy in one eye. The experimental group (group 1, n = 7) underwent i.v. injection of verteporfin and subsequent photoactivation at the operative site on postoperative day 1 (POD 1). Control groups of animals received either light exposure (group 2, n = 4) or verteporfin (group 3, n = 2), or no intervention (group 4, n = 2). Intraocular pressure (IOP) was measured prior to the procedure (POD 0) and daily thereafter for the first week after sclerectomy (PODs 1-7) and every other day for the second week (PODs 9, 11, 13, 15). Percentage IOP reductions of operated over contralateral control eyes were compared among the various groups. Success rates (percentage IOP reduction > 15%) were also compared between the experimental and control groups. Eyes were histologically examined for evaluation of fibrosis.

RESULTS

Rabbits in the experimental group (group 1) had a mean +/- SEM percentage IOP reduction of 25 +/- 3% during the follow-up period. In contrast, groups 2, 3 and 4 had IOP reductions of 4 +/- 5%, 12 +/- 7% and 4 +/- 6%, respectively (p < 0.005, anova among all four groups). Successful IOP reduction (> or = 15%) over the contralateral eye at POD 15 was achieved in six of seven experimental animals, but only in one of eight control animals (p < 0.02, chi-squared test). Bleb failure occurred significantly earlier in the control eyes compared with eyes receiving PDT (p < 0.003, log rank test). Blebs in the experimental group differed from those in the control groups histologically, lacking significant collagen deposition in the area of the sclerostomy.

CONCLUSIONS

Wound healing in glaucoma surgery may be successfully modulated postoperatively using photodynamic therapy with i.v. administered photosensitizer.

Photodynamic therapy for wound-healing modulation in pterygium surgery. A clinical pilot study

BACKGROUND

This study was performed to evaluate the safety and efficacy of photodynamic therapy with the carboxyfluorescein ester BCECF-AM as an adjunctive treatment procedure for pterygium surgery to reduce the rate of recurrence.

METHODS

In this nonrandomized prospective clinical trial, 19 eyes with nasally located primary pterygium were examined. All eyes were treated with the bare sclera surgical technique. Seven eyes received in addition treatment with BCECF-AM solution and blue light. All patients were evaluated at least after 1 day, 1 week, 1 month, 3 months, and 1 year. Postoperative fibrovascular growth from the limbus of at least 1 mm was defined as recurrence.

RESULTS

The intraoperative application of BCECF-AM solution did not cause anterior chamber flare or any other significant side effects. The bare sclera surgery rate of recurrence was 0% (zero of 12) after 3 months and 91% (11 of 12) after 1 year. The additional photodynamic therapy treatment had a rate of recurrence of 14.2% (one of seven) after 3 months and 71.4% (five of seven) after 1 year.

CONCLUSIONS

The applied PDT technique seems to be a safe procedure but is associated with a high rate of recurrence. In conclusion, the evaluated PDT treatment procedure, at this point, should not be considered. As we found a high rate of recurrence also in the control group, the bare sclera technique is not effective, even in primary pterygia.

Update on antifibrotic use in glaucoma surgery, including use in trabeculectomy and glaucoma drainage implants and combined cataract and glaucoma surgery

PURPOSE OF REVIEW

This paper summarizes the use of antifibrotic agents adjunctive to glaucoma surgery, reviews recently published studies that address current use of these antifibrotics, and reviews new methods of wound modulation.

RECENT FINDINGS

The use of antifibrotic agents, namely, 5-fluorouracil and mitomycin C, in conjunction with glaucoma surgery has resulted in lower postoperative intraocular pressures after trabeculectomy or combined cataract and glaucoma surgery. Mixed results have been seen when these agents are used with glaucoma drainage device surgery. The use of antifibrotic agents has also created and increased complications. Therefore, methods of antifibrotic use have become more refined and modified for specific circumstances. Promising new wound modulation agents, such as CAT-152, are currently under study.

SUMMARY

Antifibrotics are potent adjuncts to glaucoma surgery, but along with their beneficial use are risks that need to be considered. While we continue to look for more efficacious agents and methods to treat glaucoma, we must continue to modify techniques with the individual patient's best interest in mind.

Photodynamic modulation of wound healing in glaucoma filtration surgery

AIM

To report a clinical pilot study investigating photodynamic therapy (PDT) in combination with glaucoma filtration surgery. BCECF-AM was used as the photosensitising substance. The clinical safety and tolerability of BCECF-AM, and its efficacy in controlling postoperative intraocular pressure (IOP) were assessed.

METHODS

Before trabeculectomy (TE), 42 consecutive eyes of 36 glaucoma patients received one subconjunctival injection of 80 micro g BCECF-AM (2,7,-bis- (2-carboxyethyl) -5- (and-6) -carboxy-fluorescein, acetoxymethyl-ester) followed by an intraoperative illumination with blue light (lambda = 450-490 nm) for 8 minutes. Antifibrotic efficacy was established as postoperative IOP reduction of >20% and/or an IOP constantly < 21 mm Hg without antiglaucomatous medication. Follow up of the filtering bleb was documented by slit lamp examination.

RESULTS

Eyes had mean 1.1 preoperative surgical interventions (filtration and non-filtration glaucoma surgery). Mean preoperative IOP was 31.6 (SD 9.7) mm Hg. Patients were followed for mean 496 days (range 3.5-31.8 months). Of the 42 eyes, 25 eyes had an IOP decreased to 15.8 (3.4) mm Hg without medication (complete success: 59.5%; p<0.001; t test). Seven eyes showed good IOP reduction < 21 mm Hg under topical antiglaucomatous medication (qualified success: 16.7%). 10 eyes failed because of scarring within 2-67 weeks (23.8%). Clinical follow up examinations revealed no local toxicity, no uveitis, and no endophthalmitis.

CONCLUSIONS

This method is a new approach in modulating postoperative wound healing in human eyes undergoing glaucoma filtration surgery. The data of the first human eyes combining TE with PDT underline the clinical safety of this method and its possible potential to prolong bleb survival.