Pharmacologic induction of posterior vitreous detachment in the rabbit

A time-dependent study of nano-mechanical and ultrastructural properties of internal limiting membrane under ocriplasmin treatment

Vitreomacular traction (VMT) syndrome has only been surgically treated for a long time. Recently, enzymatic vitreolysis with ocriplasmin has emerged as a possible option to release VMT and, in some cases, close full thickness macular holes (FTMHs). Despite its clinical relevance, gathering information about the ocriplasmin-induced alterations of the Inner Limiting Membrane (ILM) of the retina in a clinical study is a complex task, mainly because of the inter-individual variability among patients. To obtain more insights into the mechanism underlying the drug action, we studied in-vitro the mechanical and morphological changes of the ILM using Atomic Force Microscopy (AFM). To this aim, we measured the ILM average Young's modulus (YM), hysteresis (H) and adhesion work (A) over time under ocriplasmin treatment. Our data unveil a time-dependent increase in the membrane YM of 19% of its initial value, along with changes in its adhesive and dissipative behavior. Such modifications well correlate with the morphological alterations detected in the AFM imaging mode. Taken all together, the results here presented provide more insights into the mechanism underlying the ocriplasmin action in-vivo, suggesting that it is only able to alter the top-most layer of the vitreal side of the membrane, not compromising the inner ILM structure.

Pharmacotherapy for Choroidal Neovascularization Due to Uncommon Causes

BACKGROUND

Choroidal neovascularization (CNV) in adults is most commonly associated with neovascular age-related macular degeneration (AMD) and pathologic myopia. Though less common, CNV can also develop from other conditions such as uveitis, central serous chorioretinopathy, angioid streaks, intraocular tumors, hereditary chorioretinal dystrophies, or can be idiopathic in origin. If left untreated, CNV may cause visual loss because of exudation of intraretinal or subretinal fluid, retinal or subretinal hemorrhage, or fibrosis involving the macula. It is well known that one of the main drivers of angiogenesis in CNV development is vascular endothelial growth factor (VEGF) and therefore inhibitors of VEGF might be an effective treatment for CNV.

METHODS

The goal of this review is to provide an overview and summary in the use of pharmacotherapy especially anti-VEGF therapy, in the treatment of CNV due to uncommon causes.

RESULTS

Results from uncontrolled case series and controlled clinical trials have reported good efficacy and safety in using anti-VEGF agents including bevacizumab, ranibizumab, aflibercept and ziv-aflibercept in the treatment of CNV due to uncommon causes. Anti-VEGF has also been used in combination with verteporfin PDT and anti-inflammatory agents for treating CNV of various causes.

CONCLUSION

Pharmacotherapy with anti-VEGF agents is an effective treatment option for CNV due to uncommon etiologies.

ARMANDODASILVA, FIALHO SILVIALIGORIO, LIBER ANDREMAURICIO, YOUNG LUCYHWAYUE, VENTURA DORAFIX. Intravitreal injection of polysorbate 80: a functional and morphological study

ABSTRACT Objective : to determine the functional and morphological effects at rabbits retina of PS80 concentration used in the preparation of intravitreal drugs. Methods: eleven New Zealand rabbits received a intravitreal injection of 0.1ml of PS80. As control, the contralateral eye of each rabbit received the same volume of saline. Electroretinography was performed according to a modified protocol, as well as biomicroscopy and retina mapping before injection and seven and ten days after. Animals were euthanized in the 30th day and the retinas were analyzed by light microscopy. Results: eyes injected with PS80 did not present clinical signs of intraocular inflammation. Electroretinography did not show any alteration of extent and implicit time of a and b waves at scotopic and photopic conditions. There were no morphological alterations of retinas at light microscopy. Conclusion: intravitreal injection of PS80 in the used concentration for intravitreal drug preparations do not cause any functional or morphological alterations of rabbit retinas. These results suggest that PS80 is not toxic to rabbit retinas and may be safely used in the preparation of new lipophilic drugs for intravitreal injection.

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?"

Pharmacologic vitreolysis with ocriplasmin: rationale for use and therapeutic potential in vitreo-retinal disorders

With increased knowledge about the origins and pathophysiology of vitreo-retinal disorders—and, in particular, the central role of anomalous posterior vitreous detachment in vitreo-maculopathies—a paradigm shift from surgery to pharmacotherapy is taking place with the development of pharmacologic vitreolysis. The first approved agent for pharmacologic vitreolysis therapy is ocriplasmin, a truncated form of the nonspecific serine protease plasmin. Twelve studies comprise the current ocriplasmin clinical trial program, demonstrating the efficacy and safety of a single intravitreal injection of ocriplasmin for the treatment of patients with symptomatic vitreo-macular adhesion or vitreo-macular traction, including patients with macular holes. Although post-approval implementation of ocriplamsin in clinical practice has shown success rates of up to 78%, there have been recent case reports of acute, transient visual dysfunction. There are thus new initiatives to further refine clinical indications for case selection and to identify possible untoward effects. Although more studies are warranted, it appears that ocriplasmin offers a good alternative to surgery. The future lies in pharmacologic vitreolysis, and the future of pharmacologic vitreolysis lies in prevention. Thus, long-term studies are needed to define a role for pharmacologic vitreolysis, in particular with ocriplasmin, in the prevention of progressive diabetic retinopathy and age-related macular degeneration.

Intravitreal autologous plasmin prepared by urokinase for vitreolysis: a pilot study

PURPOSE

To evaluate the effects of intravitreal autologous plasmin injection (IVAP) on vitreoretinal diseases and vitreolysis.

METHODS

In this interventional, prospective, case series pilot study, 8 eyes were assigned to IVAP. Plasminogen as centrifuged from the patients' plasma was converted to plasmin by adding urokinase. A total of 0.2 mL extracted plasmin was injected intravitreally. Posterior vitreous detachment (PVD) and potential injection-related complications at week 4 were the primary outcome measures. Secondary outcomes included changes in best-corrected visual acuity (VA) (logMAR) and central macular thickness (CMT).

RESULTS

Mean age of the patients was 54.35 years. Two patients had complete PVD and 3 patients had partial PVD. Four patients had decrease in CMT. The VA was not changed in 6 patients, improved in 1 patient, and decreased in 1 patient. No uveitis, endophthalmitis, or postinjection vitreous hemorrhage was observed.

CONCLUSIONS

This pilot study demonstrated the efficacy of urokinase-prepared IVAP injection on releasing vitreomacular traction and inducing vitreolysis.

Ocriplasmin for treatment of stage 2 macular holes: early clinical results

BACKGROUND AND OBJECTIVE

To review clinical and structural outcomes of ocriplasmin for treatment of stage 2 macular holes.

PATIENTS AND METHODS

A retrospective review of the first patients with stage 2 macular holes to be treated with ocriplasmin at Massachusetts Eye and Ear Infirmary. All patients were imaged with spectral-domain optical coherence tomography (SD-OCT).

RESULTS

Eight patients with stage 2 macular holes received a single injection of 125 μg of ocriplasmin. One patient (12.5%) demonstrated macular hole closure. The posterior hyaloid separated from the macula in six eyes (75%). All seven holes that remained open showed enlargement in hole diameters (narrowest, apical, and basal) at 1 week and 1 month. All seven were successfully closed with surgery. Ellipsoid zone disruptions were observed by OCT in four eyes (50%) and persisted throughout follow-up (more than 6 months on average).

CONCLUSION

In early clinical results, the authors found a lower macular hole closure rate with ocriplasmin than previously reported. Enlargement was observed in all holes that failed to close with ocriplasmin. The authors found ellipsoid zone disruptions that persisted through 6 months of follow-up after ocriplasmin injection. Further work is needed to investigate the cause for these ellipsoid zone changes.

Lens subluxation after plasmin and SF6 injections in rabbit eyes

Purpose

To investigate the rate of lens subluxation following plasmin and/or SF₆ injections in eyes, and whether a subsequent elevated level of vascular endothelial growth factor (VEGF) and vitreous tap would aggravate subluxation.

Methods

Four groups of rabbits were used. Group 1 received an intravitreal injection (IVI) of plasmin and SF₆ in the right eye; group 2 received an IVI of plasmin in the right eye; group 3 received an IVI of SF₆ in the right eye; and group 4 received an IVI of balanced salt solution in the right eye. After treatment, IVIs of VEGF were given and vitreous tap was performed three times, followed by clinical observation of lens subluxation and scanning electronic microscope evaluation of the zonular fibers.

Results

After IVIs of plasmin and SF₆, and VEGF and vitreous tap had been performed one to three times, lens subluxation was noted in 0%, 43%, 71%, 71%, and 86% of the eyes in group 1. After IVIs of plasmin, VEGF, and vitreous tap had been performed one to three times, lens subluxation was noted in 11%, 22%, 44%, 44%, and 67% of the eyes in group 2. The eyes in group 3 and 4 did not show signs of lens subluxation after VEGF IVIs and vitreous tap. Histology confirmed zonular fiber damage in the eyes treated with plasmin.

Conclusions

The incidence of lens subluxation increased following plasmin injections in the eyes, and this was aggravated by the subsequent high VEGF level in the eyes and vitreous tapping. Zonular fibers were disrupted following plasmin treatment. These effects should be kept in mind when using plasmin enzymes in patients with vitreoretinal abnormalities.

Human RPE stem cells grown into polarized RPE monolayers on a polyester matrix are maintained after grafting into rabbit subretinal space

Transplantation of the retinal pigment epithelium (RPE) is being developed as a cell-replacement therapy for age-related macular degeneration. Human embryonic stem cell (hESC) and induced pluripotent stem cell (iPSC)-derived RPE are currently translating toward clinic. We introduce the adult human RPE stem cell (hRPESC) as an alternative RPE source. Polarized monolayers of adult hRPESC-derived RPE grown on polyester (PET) membranes had near-native characteristics. Trephined pieces of RPE monolayers on PET were transplanted subretinally in the rabbit, a large-eyed animal model. After 4 days, retinal edema was observed above the implant, detected by spectral domain optical coherence tomography (SD-OCT) and fundoscopy. At 1 week, retinal atrophy overlying the fetal or adult transplant was observed, remaining stable thereafter. Histology obtained 4 weeks after implantation confirmed a continuous polarized human RPE monolayer on PET. Taken together, the xeno-RPE survived with retained characteristics in the subretinal space. These experiments support that adult hRPESC-derived RPE are a potential source for transplantation therapies.

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Adult hRPESC-derived RPE had comparable in vitro characteristics to fetal hRPE

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hRPE monolayers survived 4 weeks on PET carriers under the rabbit retina

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Better xenograft survival may be due to the maintained hRPE cell polarity

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Atrophy of the retina overlaying the hRPE xenograft remains a future challenge

[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.

Vitreomacular adhesion and neovascular age-related macular degeneration

We explore the hypothesis that vitreomacular adhesion (VMA) and vitreomacular traction (VMT) play a role in the pathogenesis and clinical course of neovascular ("wet") age-related macular degeneration (AMD). Several biological theories are offered to explain this possible association, including direct tractional force, altered vitreous oxygenation, altered diffusion coefficients of intravitreal molecules, and alterations in the pharmacokinetics of intravitreal drugs. Release of VMT may improve the clinical course of neovascular AMD, and a few case series suggest that vitrectomy can lead to both a functional and anatomic improvement. A large, randomized, controlled clinical trial is underway, investigating pharmacologic release of VMA in eyes with neovascular AMD.

Vitreomacular traction syndrome: a comparison of treatment with intravitreal plasmin enzyme vs spontaneous vitreous separation without treatment

PURPOSE

To evaluate the effects of intravitreal autologous plasmin enzyme (APE) in patients with focal vitreomacular traction (VMT).

METHODS

APE was obtained by incubation of patient-derived purified plasminogen with streptokinase, and intravitreally injected 5-12 days later. Twenty-four hours after injection, in case of incomplete VMT release, a pars plana vitrectomy was performed. The hyaloid internal limiting membrane adherence and removal of the posterior hyaloid were intraoperatively evaluated.

RESULTS

Thirteen patients were recruited. During preparation of APE, five patients had spontaneous release of VMT. Eight patients received APE injection (2 IU). In five patients, spontaneous resolution of VMT occurred before APE administration. Twenty-four hours after injection, persistence of VMT was detected in all the eight treated patients. Best-corrected visual acuity was 0.51±0.37 LogMAR at baseline, improving to 0.23±0.14 LogMAR at 6 months (P=0.002). Foveal thickness was 464±180 μm at baseline, reducing to 246±59 μm at 6 months (P<0.001). Hyaloid was intraoperatively judged 'partially detached' in seven cases and 'totally detached' in one case. Hyaloid peeling was evaluated 'easy' in six eyes and 'very easy' in two eyes.

CONCLUSIONS

In the current study, there was a large percentage of spontaneous resolution of VMT before an APE administration. A single intravitreal APE injection seems insufficient to induce a complete posterior vitreous detachment in these patients.

Vitreoretinal interface in central serous choroidopathy: a retrospective case-control study

PURPOSE

To investigate the frequency and patterns of vitreoretinal adherence in central serous choroidopathy (CSC) using spectral domain optical coherence tomography (SD-OCT) imaging and compare them with normal subject.

METHODS

A descriptive observational analytical retrospective case-control study. The study patients were split into non-chronic and chronic CSC groups and compared with an age- and gender-matched control group composed of healthy individuals without CSC. Five patterns of vitreoretinal adherence were defined: lacunae, partial posterior vitreous detachment (partial-PVD), epiretinal membrane (ERM), focal vitreomacular adherence (VMA) and no recognizable pattern. Statistical analysis was performed.

RESULTS

One hundred and four eyes of 52 patients were included in this study. Forty-eight eyes of 24 patients had chronic CSC and 56 eyes of 28 patients had non-chronic CSC. The control group for chronic CSC included 96 normal eyes of 48 subjects, and the control group for non-chronic CSC included one hundred and twelve normal eyes of 56 subjects. We found a recognizable pattern of the vitreoretinal interface (lacuna, partial-PPV, VMA or ERM) more often in non-chronic CSC (p = 0.0001, OR = 6.51 and CI = 2.71-15.62) and in chronic CSC patients (p = 0.001, OR = 4.05, CI: 1.77-9.57) than in normal subjects.

CONCLUSION

The proportion of patterns of vitreoretinal adherence and interface found in CSC changes with age and manifests differently compared with normal eyes. The results indicate early changes in CSC patients younger than 40 years of old bilaterally.

Ocriplasmin for vitreoretinal diseases

Fibronectin and laminin are clinically relevant plasmin receptors in the eye. Located at the vitreoretinal interface, they are cleaved by ocriplasmin (Microplasmin, ThromboGenics, Iselin, NJ), a novel ophthalmic medication. A series of clinical trials to study ocriplasmin for the treatment of vitreoretinal diseases such as vitreomacular traction, macular hole, and exudative age-related macular degeneration are underway. The results are promising and may impact patient care.

Diabetic macular edema: new trends in management

The treatment of diabetic macular edema may be evolving from a laser ablative approach into a pharmacotherapeutic approach. The exponential growth that has occurred over the past decade in the retinal pharmacotherapy field has led to the development of several pharmacotherapies for retinal vascular diseases such as diabetic macular edema. Many of these agents, in the form of intravitreal injections or sustained delivery devices, have already undergone clinical trial testing for safety and efficacy and many others are currently being similarly evaluated. Some of these agents have proven to be more efficacious than traditional laser therapy, and it is possible that traditional laser therapy for diabetic macular edema may be abandoned altogether in the near future, especially with the introduction of the micropulse laser. However, more research and experience is still needed in order to determine the best treatment agent or combination of therapeutic modalities, as well as the best treatment regimen for a given patient. In this article, we briefly review the major new developments in the field of diabetic macular edema treatment. In addition, we touch on some of the promising forthcoming therapies.

Enzymatic vitreolysis with ocriplasmin for vitreomacular traction and macular holes

BACKGROUND

Vitreomacular adhesion can lead to pathologic traction and macular hole. The standard treatment for severe, symptomatic vitreomacular adhesion is vitrectomy. Ocriplasmin is a recombinant protease with activity against fibronectin and laminin, components of the vitreoretinal interface.

METHODS

We conducted two multicenter, randomized, double-blind, phase 3 clinical trials to compare a single intravitreal injection of ocriplasmin (125 μg) with a placebo injection in patients with symptomatic vitreomacular adhesion. The primary end point was resolution of vitreomacular adhesion at day 28. Secondary end points were total posterior vitreous detachment and nonsurgical closure of a macular hole at 28 days, avoidance of vitrectomy, and change in best-corrected visual acuity.

RESULTS

Overall, 652 eyes were treated: 464 with ocriplasmin and 188 with placebo. Vitreomacular adhesion resolved in 26.5% of ocriplasmin-injected eyes and in 10.1% of placebo-injected eyes (P<0.001). Total posterior vitreous detachment was more prevalent among the eyes treated with ocriplasmin than among those injected with placebo (13.4% vs. 3.7%, P<0.001). Nonsurgical closure of macular holes was achieved in 40.6% of ocriplasmin-injected eyes, as compared with 10.6% of placebo-injected eyes (P<0.001). The best-corrected visual acuity was more likely to improve by a gain of at least three lines on the eye chart with ocriplasmin than with placebo. Ocular adverse events (e.g., vitreous floaters, photopsia, or injection-related eye pain--all self-reported--or conjunctival hemorrhage) occurred in 68.4% of ocriplasmin-injected eyes and in 53.5% of placebo-injected eyes (P<0.001), and the incidence of serious ocular adverse events was similar in the two groups (P=0.26).

CONCLUSIONS

Intravitreal injection of the vitreolytic agent ocriplasmin resolved vitreomacular traction and closed macular holes in significantly more patients than did injection of placebo and was associated with a higher incidence of ocular adverse events, which were mainly transient. (Funded by ThromboGenics; ClinicalTrials.gov numbers, NCT00781859 and NCT00798317.).

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.

Intravitreal injection of autologous plasmin enzyme for macular edema associated with branch retinal vein occlusion

PURPOSE

To investigate the effects of an intravitreal injection of autologous plasmin enzyme for macular edema associated with a branch retinal vein occlusion (BRVO).

DESIGN

Prospective, interventional case studies.

METHODS

Twenty-six eyes of 26 patients (14 men and 12 women) with macular edema resulting from a BRVO were studied. None of the eyes had a posterior vitreous detachment (PVD). The average age at the onset of BRVO was 58.7 ± 6.6 years. The interval between onset of the macular edema and injection of autologous plasmin enzyme was 4.2 months. One international unit of autologous plasmin enzyme in 0.1 mL was injected into each vitreous. The presence of a PVD was evaluated 1 week after the injection, and the visual acuity and macular thickness were measured before and 1 week and 1, 3, 6, and 12 months after the autologous plasmin enzyme injection.

RESULTS

After the autologous plasmin enzyme injection, a total PVD was observed in 23 eyes and no PVD was observed in 3 eyes. The visual acuity gradually recovered after the injection, improved by 2 lines or more in 23 eyes, and remained unchanged in the 3 eyes. The retinal thickness also recovered gradually at 1, 3, 6, and 12 months. The mean retinal thickness was reduced from 602.12 to 253.62 μm at 12 months after surgery. It was reduced significantly after 1, 3, 6, and 12 months (P < .0001).

CONCLUSIONS

Intravitreal autologous plasmin enzyme may lead to an improvement of visual acuity and a reduction of macula edema in eyes with BRVO.

Efficacy of plasmin, microplasmin, and streptokinase-plasmin complex for the in vitro degradation of fibronectin and laminin- implications for vitreoretinal surgery

PURPOSE

Plasmin enzyme generates vitreoretinal separation by degradation of laminin and fibronectin in the vitreoretinal interface. It can be activated from plasminogen by urokinase, tissue plasminogen activator, or by formation of a 1:1 complex with streptokinase. The latter is then converted into a streptokinase-plasmin-complex (SK-P), which displays fibrinolytic activity and can generate free plasmin by proteolysis of plasminogen. We compared the efficacy of SK-P, SK-P activated plasmin, urokinase activated plasmin (UK-P), and microplasmin, a truncated form of plasmin, in cleaving laminin and fibronectin.

METHODS

Streptokinase (SK) was added to human plasminogen in molar ratios between 1:100 and 2:1, generating SK-P at ratios > 1:1, and mixtures of SK-P and free plasmin (SK-P/plasmin) at lower ratios. SK-PL, SK-P/plasmin, UK-P, and microplasmin were added to laminin and fibronectin, incubated at 37 degrees C for 30 min-22 hr and processed for SDS-PAGE.

RESULTS

Proteolysis using SK-activated plasminogen increased when the SK/plasminogen ratio was decreased, generating increasing amounts of free plasmin. Microplasmin and urokinase-activated plasmin displayed similar proteolysis of both laminin and fibronectin as SK/plasminogen at ratios of 1:10 or lower.

CONCLUSION

The mode of plasminogen activation influences the efficacy of proteolysis for laminin and fibronectin and should be considered when plasmin is used in vitreoretinal surgery.

Differential vitreous dye diffusion following microplasmin or plasmin pre-treatment

PURPOSE

Plasmin and microplasmin are related enzymes that differ mainly in size. The differential effect of plasmin and microplasmin on vitreous structure, protein degradation, and dye diffusion through porcine vitreous was evaluated.

METHODS

The enzymatic effect was examined using a number of approaches on fresh porcine eyes: (1) structural integrity of vitreous after a 2-hr incubation using the electron microscope (EM); (2) effect on soluble proteins within the vitreous using gel electrophoresis after incubation at various time points over a 24-hr period; (3) fluorescein dye diffusion within the vitreous cavity measured over a 1-hr period following a 2-hr incubation. The chosen enzymatic activities for plasmin 0.5 IU and microplasmin 125 microg were within the clinical range, and were chosen for equipotence. A saline control was also used in all experiments.

RESULTS

Significant structural changes were seen with both microplasmin and plasmin when examined by EM. Gel electrophoresis showed that microplasmin and plasmin digested the same proteins, mainly molecular weights above 50 kDa. The enzymatic effect was noticeable earlier in microplasmin-treated eyes and was more significant by the end of the incubation period. Differential fluorescein diffusion rates were seen between normal saline, plasmin, and microplasmin within the vitreous cavity. The greatest diffusion rate was seen with microplasmin and was statistically significantly higher than plasmin.

CONCLUSION

Microplasmin and plasmin have a similar enzymatic effect on vitreous. However, an equipotent amount of microplasmin appears to have a more extended effect on vitreous gel. This may, in part, be related to its smaller size allowing it to diffuse more readily through the vitreous matrix.

A placebo-controlled trial of microplasmin intravitreous injection to facilitate posterior vitreous detachment before vitrectomy

PURPOSE

To evaluate the safety and efficacy of a preoperative intravitreous injection of microplasmin in patients scheduled for vitreous surgery.

DESIGN

Phase 2, multicenter, placebo-controlled, double-masked, parallel-group, dose-ranging clinical trial.

PARTICIPANTS

One hundred twenty-five patients scheduled for pars plana vitrectomy (PPV), primarily for treatment of either vitreomacular traction or macular hole.

INTERVENTION

A single intravitreous injection of either microplasmin at 1 of 3 doses (25 microg, 75 microg, or 125 microg in 100 microl) or placebo injection administered 7 days before PPV.

MAIN OUTCOME MEASURES

Presence or absence of posterior vitreous detachment (PVD) at the time of PPV, progression of PVD, and resolution of vitreomacular interface abnormality precluding the need for PPV.

RESULTS

Rates of total PVD at the time of surgery were 10%, 14%, 18%, and 31% in the placebo group (n = 30), 25-microg (n = 29), 75-microg (n = 33), and 125-microg microplasmin groups (n = 32), respectively. The secondary end point resolution of vitreomacular interface abnormality precluding the need for vitrectomy at the 35-day time point was observed at rates of 3%, 10%, 15%, and 31% in the placebo, and the 25-microg, the 75-microg, and the 125-microg microplasmin groups, respectively. At the 180-day time point, the equivalent rates were 3%, 7%, 15%, and 28%, respectively.

CONCLUSIONS

Microplasmin injection at a dose of 125 microg led to a greater likelihood of induction and progression of PVD than placebo injection. Patients receiving microplasmin were significantly more likely not to require vitrectomy surgery. More definitive evaluation in phase 3 clinical trials therefore is warranted.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

Herpes simplex virus entry receptor nectin-1 is widely expressed in the murine eye

PURPOSE

Nectin-1 belongs to the immunoglobulin superfamily, mediates cell-cell adhesion in cadherin-based adherens junctions, and acts as a receptor for herpes simplex virus (HSV). The goals of this study were (1) to determine whether nectin-1 is expressed in ocular tissue that is an important target of HSV infections and (2) to determine whether HSV type 1 (HSV-1) infection affects nectin-1 expression in the eye.

METHODS

Expression of nectin-1 and HSV-1 protein was determined by immunohistochemical analysis of ocular tissues of untreated BALB/c mice and mice that were euthanized either 7 days or 7 months after corneal inoculation of HSV-1 or sterile tissue-culture medium (mock).

RESULTS

In ocular tissues derived from untreated and mock-infected mice, widespread nectin-1 expression was detected among cells of the corneal epithelium and endothelium, conjunctiva, lens epithelium, ciliary body, iris, choroid, and retina. However, fibroblasts in the corneal stroma and the sclera did not express detectable levels of nectin-1. Ocular tissues from mice euthanized 7 days after corneal inoculation of HSV-1 frequently demonstrated corneal ulceration and inflammation and HSV-1 protein expression in the corneal epithelium, stroma, endothelium, conjunctiva, iris, and ciliary body but rarely in the retina. Ocular tissues from mice euthanized 7 months after HSV-1 inoculation demonstrated corneal epithelial and stromal inflammation, but HSV-1 protein expression was not detected. HSV-1 infection did not lead to a loss of nectin-1 expression in any of the tissues examined. In contrast to uninfected corneas, the inflamed and vascularized stroma of infected corneas contained mononuclear inflammatory cells, vascular cells, and fibroblasts that stained positive for nectin-1.

CONCLUSIONS

Findings report that nectin-1 is widely expressed in murine ocular tissues. Only fibroblasts in the corneal stroma and sclera of uninfected tissues were devoid of nectin-1 expression. HSV-1-infected inflamed corneas contained some stromal fibroblasts with detectable nectin-1 expression, which potentially could be targeted by the virus. Widespread nectin-1 expression in the eye suggests that this receptor may play a role in the pathogenesis of ocular HSV infections.

Microplasmin intravitreal administration in patients with vitreomacular traction scheduled for vitrectomy: the MIVI I trial

PURPOSE

To evaluate the safety and preliminary efficacy of 4 doses and several exposure times of intravitreal microplasmin given before pars plana vitrectomy for vitreomacular traction maculopathy.

DESIGN

A multicenter, prospective, uncontrolled, dose-escalation, phase I/II clinical trial.

PARTICIPANTS

Sixty patients enrolled into 6 successive cohorts.

INTERVENTION

A single intravitreal injection of microplasmin at 1 of 4 doses (25, 50, 75, or 125 microg in 100 microl) administered either 1 to 2 hours, 24 hours, or 7 days before planned pars plana vitrectomy.

MAIN OUTCOME MEASURES

For safety, a complete ophthalmologic examination, fundus photography, fluorescein angiography, Humphrey visual fields, and electrophysiology; for efficacy, posterior vitreous detachment (PVD) induction as assessed by B-scan ultrasound and ease of PVD induction at the time of vitrectomy.

RESULTS

The use of microplasmin led to a progressively higher incidence of PVD induction on ultrasonography with increasing time exposure. A PVD before surgery was observed with 25 microg microplasmin in 0, 2, and 5 patients with increasing exposures (2 hours, 24 hours, 7 days). With increasing dose, a PVD before surgery was observed by ultrasound as follows: 25 microg, 0; 50 microg, 1; 75 microg, 2; 125 microg, 3. However, at surgery, with a 125-microg dose, these patients had a discontinuous layer of vitreous present on the retinal surface resulting from the induction of an anomalous PVD in the form of vitreoschisis. One retinal detachment developed shortly after administration of microplasmin. Two developed after surgery. There were no other safety concerns.

CONCLUSIONS

Results from this initial clinical trial evaluating intravitreal microplasmin show the drug to be well tolerated and capable of inducing a pharmacologic PVD in some patients. These results warrant evaluation of microplasmin in larger, controlled trials.

Pharmacologic vitreolysis with plasmin and hyaluronidase in diabetic rats

OBJECTIVE

To evaluate the feasibility of inducing posterior vitreous detachment (PVD) with pharmacologic vitreolysis in diabetic rats.

METHODS

Forty diabetic rats were randomly divided into four groups and treated with different drugs by intravitreous injection respectively as follows: Group A: hyaluronidase (5 U); Group B: plasmin (0.25 U); Group C: hyaluronidase (5 U) plus plasmin (0.25 U); and Group D: balanced salt solution (2 microL). Ten normal rats in Group E were used as controls and were treated with hyaluronidase (5 U) plus plasmin (0.25 U). Clinical observation, visual electrophysiology tests (electroretinogram), transmission electron microscopy, and scanning electron microscopy were performed on the rats 1 week after the injection.

RESULTS

Scanning electron microscopy results showed that PVD did not occur at all with hyaluronidase alone (Group A, 0 of 10) and balanced salt solution alone (Group D, 0 of 10). Partial PVD was found in all eyes treated with plasmin alone (Group B, 10 of 10), whereas complete PVD was present in most but not all eyes treated with both hyaluronidase and plasmin (Group C, 8 of 10). All nondiabetic eyes treated with hyaluronidase and plasmin had total PVD (Group E, 10 of 10). No significant difference in electroretinogram was observed in each group before and after the injection (P < 0.05).

CONCLUSION

Hyaluronidase (5 U) alone is ineffective, whereas plasmin (0.25 U) alone induces partial PVD, a very dangerous state for the diabetic eye. Combination of hyaluronidase and plasmin can induce complete PVD in 12-week old diabetic rats. However, it is more difficult to induce PVD in diabetic rats than in healthy rats. No obvious toxic reaction was observed in each group.

Effect of intravitreal plasmin on vitreous removal through a 25-gauge cutting system in the rabbit in vivo

PURPOSE

Intravitreal plasmin creates a posterior vitreous detachment, but may also liquefy the vitreous. This study measures the rate of vitreous removal from rabbit eyes after plasmin injection in vivo.

METHODS

Intravitreal injections of 150 IU hyaluronidase (n = 5), 0.5 activity units (AU, n = 6) or 0.9 AU of streptokinase-activated human plasmin (n = four groups of 6) in 0.1 ml were performed in rabbits, the fellow eyes received 0.1 ml BSS. After 30 min (hyaluronidase), 30 min, 4 h, 12 h or 24 h (0.9 AU plasmin) or 24 h (0.5 AU plasmin), 1 ml of vitreous was removed from each eye without infusion, using a 25-gauge cutter and a standardized protocol. Animals were sacrificed after surgery.

RESULTS

Compared to fellow eyes, the average rate of vitreous removal was increased by hyaluronidase by 68.9 +/- 6.3% (p < 0.05) and by 0.5 AU plasmin (24 h) by 26.8 +/- 3.3% (p < 0.05). 0.9 AU of plasmin increased removal rates by 0.8 +/- 10% (n.s.), 15.4 +/- 6.3% (p < 0.05), 40.3 +/- 3.1% (p < 0.05), and 71.9 +/- 32.4% (p < 0.05) after 30 min, 4 h, 12 h and 24 h incubation respectively. The ratios of removal rates of treated/control eyes in the 0.9 AU groups showed a linear correlation with incubation time (r = 0.783, p < 0.0001).

CONCLUSION

Intravitreal plasmin increases the rate of vitreous removal in rabbits.

Nonclinical safety and pharmacokinetics of intravitreally administered human-derived plasmin in rabbits and minipigs

The use of plasmin for pharmacologic vitreolysis and the creation of a posterior vitreous detachment offers several potential advantages over surgery. The nonclinical pharmacokinetics and safety of human-derived plasmin was evaluated following single or multiple intravitreal injections to rabbits and minipigs. Single intravitreal injections of plasmin at 45-900 microg resulted in a no adverse effect level (NOAEL) of 45 microg in both species; effects at higher doses included chemosis, mucopurulent discharge, mononuclear cell infiltrates in the iris-ciliary body, and reversible changes in electroretinogram waveforms and parameters. No retinal histopathology abnormalities were observed. Following 4 weekly intravitreal injections at 4-423 microg, a NOAEL of 4 microg was identified. Effects at the higher doses included myosis, iritis, iridolenticular synechiae, and changes in electroretinogram waveforms and parameters that were generally not reversible in the present investigation. Vitreal plasmin concentrations were highest at 30 min after dosing and decreased rapidly; measurable concentrations remained, in some animals, at 24 h. Intravitreal plasmin exposure increased in a less-than-dose-proportional manner and tended to be lower in minipigs than in rabbits. The current findings demonstrate acceptable nonclinical safety and pharmacokinetics of intravitreal human plasmin in rabbits and minipigs and support the clinical development of plasmin for ocular diseases.

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.

Microplasmin-induced posterior vitreous detachment affects vitreous oxygen levels

PURPOSE

To determine if enzymatic induction of a posterior vitreous detachment (PVD) and/or vitreous liquefaction affects O2 concentration in the vitreous cavity in animals with vascularized and avascular retinal circulations.

METHODS

Either microplasmin or hyaluronidase was injected intravitreally into guinea pigs (avascular retinal circulation), brown Norway rats (vascularized retinal circulation without fovea), or cats (vascularized retinal circulation with fovea) with the contralateral eye used as a control. One to 2 weeks post injection, vitreal oxygen concentration was measured using a highly sensitive, platinum-based fluorophore O2 sensor. In addition, control and microplasmin-injected rats, guinea pigs, and cats were exposed to 100% oxygen and vitreal O2 levels were measured over time. Scanning electron microscopy (SEM) was used to evaluate the vitreoretinal interface for the presence of a PVD.

RESULTS

In animals with a vascularized retinal circulation (brown Norway rats and cats), intravitreal injection of microplasmin with induction of a PVD significantly increased baseline O2 concentration in the vitreous cavity compared to hyaluronidase injected eyes and controls in rats (35, 25, and 23 mm Hg, P < 0.001 and P < 0.001, respectively) and cats (26, 18, and 16 mm Hg, P < 0.01 and P < 0.001, respectively). Interestingly, intravitreal injection of hyaluronidase (vitreous liquefaction without induction of a PVD) did not significantly increase vitreal O2 levels in any of the animal species (P > 0.1). Upon exposure to 100% oxygen by facemask, microplasmin injected animals showed a rapid increase in vitreal oxygen levels compared to hyaluronidase injected animals and controls, indicating that the presence of a PVD allows rapid O2 exchange within the vitreous cavity. Similarly, once O2 was discontinued, the O2 concentration decreased in a similarly rapid rate. SEM showed smooth retinal surfaces in microplasmin-injected cat eyes, indicating the presence of a PVD which was not present in hyaluronidase injected or control eyes.

CONCLUSION

The results suggest that enzymatic-assisted PVD with microplasmin increases vitreal O2 levels and increases the rate of O2 exchange within the vitreous cavity.

Plasmin enzyme-assisted vitreoretinal surgery in congenital X-linked retinoschisis: surgical techniques based on a new classification system

PURPOSE

To review the surgical outcome of autologous plasmin enzyme-assisted vitreoretinal surgery in managing complications associated with congenital X-linked retinoschisis (CXLRS).

METHODS

Medical records of 20 patients (22 eyes) with CXLRS complications, treated with autologous plasmin enzyme-assisted vitreoretinal surgery, were reviewed. Surgical techniques were adapted according to a new CXLRS classification.

RESULTS

Median age of the cohort was 3.5 years. Indications for surgical intervention included 8 eyes with schisis involving or threatening the macula, 7 eyes with rhegmatogenous retinal detachment, 4 eyes with tractional retinal detachment, 1 eye with vitreous and intraschisis hemorrhage, 1 eye with obstruction of the macula by an overhanging bullous schisis cavity, and 1 eye with macular pucker. Ninety-one percent (20/22) of eyes had retinal attachment postoperatively after an average of 1.3 procedures per eye. Of the eyes in which visual acuity was measured, 53% (8/15) improved, 33% (5/15) had no change, and 13% (2/15) lost vision.

CONCLUSION

Plasmin enzyme-assisted vitreoretinal surgery is a safe and effective method for managing the complications associated with CXLRS. Most patients had improved or stable postoperative visions.

Pediatric traumatic macular hole: results of autologous plasmin enzyme-assisted vitrectomy

PURPOSE

To review our experience with plasmin-assisted vitrectomy surgery for the treatment of pediatric macular holes.

DESIGN

Retrospective, interventional case series.

METHODS

Thirteen pediatric patients aged one to 15 years with a traumatic macular hole underwent surgical repair. All patients underwent surgery between February 1997 and March 2005 with autologous plasmin enzyme-assisted vitrectomy. After induction of posterior vitreous detachment (PVD), vitrectomy with membrane peeling and gas or silicone oil injection were performed followed by prone positioning for seven days. Main outcome measures included anatomic closure rate, visual outcome, and ocular complications.

RESULTS

The macular hole was closed successfully in 12 (92%) of 13 cases. Of the 12 patients for whom vision could be measured, 11 patients (92%) had visual acuity improvement of 2 or more lines and six patients (50%) achieved vision of 20/50 or better; all of the patients achieved vision better than 20/200. The visual improvement was statistically significant (P = .005, Wilcoxon signed-rank test). Surgical complications included cataract formation in one patient and retinal detachment in one patient.

CONCLUSIONS

Autologous plasmin enzyme may be a helpful adjunct when performing vitrectomy for traumatic macular holes.

Enzymatic vitreolysis with recombinant microplasminogen and tissue plasminogen activator

PURPOSE

To generate microplasmin (microPlm) using recombinant microplasminogen (microPlg) and recombinant tissue plasminogen activator (rt-PA) before intravitreous injection and to investigate the efficacy of microPlm in inducing posterior vitreous detachment (PVD).

METHODS

Forty-eight female or male New Zealand white rabbits were randomized into three groups. Recombinant human microPlg was incubated with rt-PA with a 200:1 molar ratio at 37 degrees C for 40 min. The right eyes of groups 1, 2, and 3, were injected with 0.5, 1.0, and 1.5 U microPlm in 0.1 ml respectively, and 0.1 ml balanced salt solution (BSS) was injected into the left eye as controls. Scanning electron microscopy (SEM), gross specimen examination, B-ultrasonography and optical coherence tomography (OCT) were performed to detect vitreoretinal interface.

RESULTS

Over eighty percent of recombinant human microPlg could be activated to active microPlm by rt-PA after 40 min incubation. Complete PVD was found at vitreous posterior pole of microPlm-treated eyes without morphological change of retina. Complete PVD of 25, 75, and 87.5% rabbit eyes was induced by 0.5, 1.0 and 1.5 U recombinant microPlm respectively on day 1. The remnants of vitreous cortex at the posterior pole were dependent on the concentration of microPlm. Among the four approaches for detecting PVD, SEM, gross specimen examination, and B-ultrasonography were more effective methods than OCT.

CONCLUSION

Intravitreous injection of 1.5 U microPlm can effectively induce complete PVD in rabbit eyes on day 1 without morphological change of retina.