Intravitreal injection of dispase causes retinal hemorrhages in rabbit and human eyes

From the analysis of pharmacologic vitreolysis to the comprehension of ocriplasmin safety

INTRODUCTION

Pharmacologic vitreolysis is a strategy used to treat anomalous posterior vitreous detachment, by weakening vitreoretinal adhesion with an intravitreal drug. Pharmacologic vitreolysis facilitates surgery, and abnormalities of the vitreoretinal interface including vitreomacular traction (VMT) and early stage macular hole (MH) could be resolved. Ocriplasmin is a recombinant protease, active against fibronectin and laminin, which are important components of the vitreoretinal interface. Ocriplasmin has been approved for symptomatic treatment of VMT and MH with visible traction, and it functions by dissolving the proteins that link the vitreous to the macula, thereby creating a complete posterior vitreous detachment (PVD).

AREAS COVERED

This paper reviews the current knowledge and status of investigations regarding the use of ocriplasmin for pharmacologic vitreolysis and its safety.

EXPERT OPINION

Ocriplasmin is a non-specific enzyme; therefore, it dissolves vitreal proteins as well as possibly proteins associated with visual function in the retina, choroid, and lens. Ocular adverse events (OAEs) of ocriplasmin include transient visual loss, intraocular inflammation, vitreous floaters, lens opacification, zonular instability of the lens, and intraocular hemorrhage. The prevalence of the OAEs is very low; however, on rare occasions, they can result in widespread retinal dysfunction. Research into the acute and long-term safety of ocriplasmin is required.

Ocriplasmin: who is the best candidate?

Enzymatic vitreolysis is currently the focus of attention around the world for treating vitreomacular traction and full-thickness macular hole. Induction of posterior vitreous detachment is an active area of developmental clinical and basic research. Despite exerting an incompletely elucidated physiological effect, ocriplasmin (also known as microplasmin) has been recognized to serve as a well-tolerated intravitreal injection for the treatment of vitreomacular traction and full-thickness macular hole. There are several unexplored areas of intervention where enzymatic vitreolysis could potentially be used (ie, diabetic macular edema). Recent promising studies have included combinations of enzymatic approaches and new synthetic molecules that induce complete posterior vitreous detachment as well as antiangiogenesis. Although no guidelines have been proposed for the use of ocriplasmin, this review attempts to aid physicians in answering the most important question, "Who is the best candidate?"

Induction of Posterior Vitreous Detachment in Pediatric Vitrectomy by Preoperative Intravitreal Injection of Tissue Plasminogen Activator

PURPOSE

To report the efficacy of intravitreal injection of tissue plasminogen activator (tPA) with or without autoserum in induction of posterior vitreous detachment (PVD) in pediatric vitrectomy.

METHODS

Retrospective, interventional case series of pediatric patients receiving intravitreal injection of tPA preoperatively to facilitate PVD in vitrectomy from January 2011 to December 2014 at the Changhua Christian Hospital, Taiwan. All patients received intravitreal injections of 25 µg of tPA 3 days before vitrectomy. For cases without preexisting vitreous hemorrhage, 0.1 mL of intravitreal autologous serum was co-administered. Main outcome measures included successful rate of posterior vitreous detachment in vitrectomy, visual outcome, and related ocular complications.

RESULTS

Four boys and 2 girls were included. Ages ranged from 39 weeks' postmenstrual age to 8 years. The indications for vitrectomy were traumatic macular hole (cases 1 and 2); premacular hemorrhage secondary to retinopathy of prematurity (case 3); abusive head trauma with premacular hemorrhage, subinternal limiting membrane hemorrhage, and macular hole (case 4); trauma with dense vitreous hemorrhage (case 5); and vitreous hemorrhage with unknown cause (case 6). Successful PVD was induced intraoperatively in all cases and the macular hole was closed successfully in 3 of 3 cases (cases 1, 2, and 4). No surgical complications were noted. Visual outcome improved in all 3 eyes with checkable preoperative visual acuity (cases 1, 2, and 6).

CONCLUSIONS

Intravitreal injection of tPA 3 days before vitrectomy may be a helpful adjunct to induce pediatric PVD.

[Pharmacological vitreolysis]

Posterior vitreous detachment (PVD) is a physiological ageing process. In many cases PVD is incomplete and pathological adhesions of vitreous collagen may be associated with tractional forces in the periphery where they can cause retinal breaks and lead to detachment of the neurosensory retina. In the macular area such tractional forces at the vitreoretinal interface can contribute to the formation of specific entities such as vitreomacular traction syndrome and macular holes which are associated with an impairment of visual acuity and disturbing metamorphopsia. Currently, pars plana vitrectomy with induction of PVD, peeling of epiretinal membranes and the ILM represents an effective and safe treatment option for these conditions. Pharmacological vitreolysis is a new and alternative, non-surgical approach to release tractional forces at the vitreoretinal interface by injecting an enzyme with proteolytic activity against fibronectin and laminin into the vitreous cavity. Certain forms of vitreomacular traction and smaller macular holes can be successfully treated in this way without surgical manipulation of the retinal surface. The role of the concept of pharmacological vitreolysis as a treatment option even for exudative macular diseases or as an adjunct to assist vitreoretinal surgical procedures is currently under investigation.

Review and perspectives on pharmacological vitreolysis

The vitreous is involved in multiple diseases when an incomplete posterior vitreous detachment (PVD) occurs. An incomplete PVD can lead to several pathological conditions. Such visually threatening conditions are traditionally of exclusive surgical interest. In contrast, pharmacological vitreolysis is the effort to reduce or eliminate the pathogenetic role of the vitreous solely by means of drug delivery. Here we aim to review and summarize the evidence available to date about this challenging new approach.

Microplasmin (ocriplasmin) in pediatric vitreoretinal surgery: update and review

PURPOSE

To discuss the potential role of microplasmin (ocriplasmin) as a surgical adjunct to vitrectomy in pediatric vitreoretinopathies.

METHODS

Literature review of the laboratory and clinical evidence to date for the use of both autologous plasmin enzyme as an adjunct to vitrectomy and more recently recombinant microplasmin (ocriplasmin) as monotherapy for focal vitreomacular traction in adults.

RESULTS

Autologous plasmin enzyme is currently being used as a surgical adjunct to vitrectomy, with supporting Levels 2 and 3 published evidence in a range of pediatric vitreoretinopathies including Stage 5 retinopathy of prematurity and congenital X-linked retinoschisis. The availability of autologous plasmin enzyme is limited. In recent Phase 3 clinical trials, intravitreal ocriplasmin versus sham injection resulted in resolution of focal vitreomacular traction in 27% versus 10% (P < 0.001, n = 652).

CONCLUSION

Ocriplasmin may potentially be used as a surgical adjunct to vitrectomy in place of autologous plasmin enzyme. A Phase 2, randomized, placebo-controlled surgical trial is under way to assess this.

Emerging nonsurgical methods for the treatment of vitreomacular adhesion: a review

With the dissemination of optical coherence tomography over the past two decades, the role of persistent vitreomacular adhesion (VMA) in the development of numerous macular pathologies - including idiopathic macular hole, vitreomacular traction syndrome, cystoid and diabetic macular edema, neovascularization in diabetic retinopathy and retinal vein occlusion, exudative age-related macular degeneration, and myopic traction maculopathy - has been established. While invasive vitreoretinal procedures have long been utilized to address complications related to these disorders, such an approach is hampered by incomplete vitreoretinal separation and vitreous removal, surgical complications, and high costs. In light of such limitations, investigators have increasingly looked to nonsurgical means for the treatment of persistent pathologic VMA. Chief among these alternative measures is the intravitreal application of pharmacologic agents for the induction of vitreous liquefaction and/or vitreoretinal separation, an approach termed pharmacologic vitreolysis. This article aims to review the available evidence regarding the use of pharmacologic agents in the treatment of VMA-related pathology. In addition, a discussion of vitreous molecular organization and principles of physiologic posterior vitreous detachment is provided to allow for a consideration of vitreolytic agent mode of action and molecular targets.

Enzymatic vitreous disruption

Enzymatic vitreous disruption refers to cleaving the vitreoretinal junction by enzymatic means, thereby inducing posterior vitreous detachment (PVD) and liquefaction of the vitreous gel. Several enzymes have been proposed in this respect, including chondroitinase, hyaluronidase, dispase, and plasmin. In an experimental setting, chondroitinase induced PVD and was helpful in removing epiretinal membranes but no further data have been reported yet. Hyaluronidase liquefies the vitreous as demonstrated in a phase III trial in diabetic patients with vitreous haemorrhage. Dispase induces PVD but also causes inner retinal damage and is now used as an animal model of proliferative vitreoretinopathy. Plasmin has the capability of both PVD induction and liquefaction. However, plasmin is highly unstable and not available for clinical use. Microplasmin (ThromboGenics Ltd, Dublin, Ireland) is a truncated form of human plasmin sharing the same catalytic activity like plasmin. Recombinant microplasmin is under clinical investigation in patients with vitreomacular traction. This review article reports on the current knowledge of enzymatic vitreous disruption and discusses details of the enzyme candidates in basic and clinical research terms.

PVD following plasmin but not hyaluronidase: implications for combination pharmacologic vitreolysis therapy

PURPOSE

To study whether intravitreal injection of plasmin + hyaluronidase safely induces posterior vitreous detachment (PVD).

METHODS

Rabbits were randomized into three groups: (A) 20 rabbits, intravitreal injection of plasmin 1 U + hyaluronidase 20 U in balanced salt solution (BSS) 0.1 mL into one eye; (B) 12 rabbits, plasmin alone; (C) 12 rabbits, hyaluronidase alone. The fellow eye of each rabbit was injected BSS 0.1 mL. In Group A, scanning electron microscopy (SEM) was done in four rabbits at 0.5 hour and in four rabbits at 1 hour. After 7 days, all the remaining 36 rabbits received electroretinography, SEM was examined in eight of each group, and immunohistochemistry was done in four of each group.

RESULTS

SEM disclosed the eyes of Group A had complete PVD (8/8), Group B partial PVD (7/8), and Group C (8/8) and all the control eyes (24/24) no PVD after 7 days. Partial PVD was found in 4/4 at 0.5 hour and complete PVD was seen in 3/4 at 1 hour in Group A. Immunohistochemistry showed that the amounts of laminin and fibronectin in the vitreoretinal interface were decreased in Group A and B versus the control eyes (P <0.001), but not in Group C versus the control eyes (P >0.05). Electroretinography showed no changes in any group (P >0.05).

CONCLUSION

Vitreous injection of plasmin + hyaluronidase induced complete PVD with no obvious toxicity. Plasmin induced partial PVD, but hyaluronidase had no effects.

Enzyme-assisted vitrectomy in enucleated pig eyes: a comparison of hyaluronidase, chondroitinase, and plasmin

PURPOSE

Facilitation of vitrectomy by vitreolytic enzymes may be of great value in complicated or office-procedure vitreo-retinal surgery. In this study, we quantified and compared the effect of hyaluronidase, chondroitinase, and plasmin pre-incubation on vitrectomy rate and explored potential retinal damage.

METHODS

Freshly enucleated pigs eyes were incubated (1 or 3 hours) with an intravitreally injected enzyme or control solution. Enzyme doses were 100 and 1000 U for hyaluronidase, 1 and 2 U for chondroitinase, 3 and 30 U for plasmin. The eyes were weighed before and after 10 minutes of one-port vitrectomy, the difference representing the amount of removed vitreous. Light microscopy was used to assess potential damage to the retina.

RESULTS

All enzymes significantly increased the amount of removed vitreous at all doses and incubation periods. The highest increase was found with hyaluronidase 1000 U, 3 hours, the lowest with chondroitinase 1 U, 1 hour. Damage occasionally occurred to the internal limiting membrane and very rarely to the nerve fiber layer. No damage at all was seen in the 100 and 1000 U hyaluronidase (1-hour incubation) groups.

CONCLUSIONS

Hyaluronidase, chondroitinase, and plasmin are good candidates for enzyme-assisted vitrectomy. Although retinal structural damage was very rarely seen, safety concerns will have to be investigated further.

Amniotic membrane maintains the phenotype of rabbit retinal pigment epithelial cells in culture

The success of surgical removal of choroidal neovascularisation followed by transplantation of autologous retinal pigment epithelial cells (RPE) for age-related macular degeneration (ARMD) may be limited by damage in Bruch's membrane. We investigated whether amniotic membrane (AM) might be used as an alternative basement membrane-containing matrix to support RPE growth and differentiation. Primary RPE plastic cultures were established from freshly enucleated Dutch belted rabbit eyes in DMEM/F12 containing 0.1 mM Ca(++) and 10% dialysed FBS. Upon subconfluence, cells were subcultured at 5000-9000 cells cm(-2) in the above-mentioned culture medium on intact AM (iAM), epithelially denuded AM (dAM) or plastic. After confluence, the Ca(++) concentration in the medium was increased to 1.8 mm for 4 weeks. Growth and morphology were monitored by phase contrast microscopy, and the phenotype by immunostaining with antibodies against cytokeratin 18, tight junction protein ZO-1, and RPE65 protein, and by transepithelial resistance (TER) measurement. Immunostaining to cytokeratin 18 confirmed the epithelial origin of isolated cells in both primary culture and subcultures. Compared to plastic cultures, RPE increased pigmentation within 24 hr after seeding on AM, with iAM being more pronounced than dAM. RPE adopted a hexagonal epithelial phenotype with more organised pigmentation, strong expression of ZO-1 and RPE65, and a significantly higher TER 4 weeks after Ca(++) switch on dAM. Our results indicate that AM may be used as a basement membrane-containing matrix to maintain RPE phenotype in vitro, and may facilitate subsequent transplantation to treat ARMD.

Anomalous posterior vitreous detachment: a unifying concept in vitreo-retinal disease

Posterior vitreous detachment (PVD) is the consequence of changes in the macromolecular structure of gel vitreous that result in liquefaction, concurrent with alterations in the extracellular matrix at the vitro-retinal interface that allow the posterior vitreous cortex to detach from the internal limiting lamina of the retina. Gel liquefaction that exceeds the degree of vitro-retinal dehiscence results in anomalous PVD (APVD). APVD varies in its clinical manifestations depending upon where in the fundus vitreo-retinal adhesion is strongest. At the periphery, APVD results in retinal tears and detachments. In the macula, APVD causes vitreo-macular traction syndrome, results in vitreoeschisis with macular pucker or macular holes, or contributes to some cases of diabetic macular edema. At the optic disc and retina, APVD causes vitreo-papillary traction and promotes retinal and optic disc neovascularization. Unifying the spectrum of vitreo-retinal diseases into the conceptual frame-work of APVD underscores that to more effectively treat, and ultimately prevent, these disorders it is necessary to replicate the two components of an innocuous PVD, i.e., gel liquefaction and vitreo-retinal dehiscence. Pharmacologic vitreolysis is designed to mitigate against APVD by chemically breaking down vitreous macromolecules and weakening vitro-retinal adhesion to safely detach the posterior vitreous cortex. This would not only facilitate surgery, but if performed early in the natural history of disease, it should prevent progressive disease.