The vitreous gel: more than meets the eye

Effects of core vitrectomy in the treatment of age-related macular degeneration

PURPOSE

To investigate the clinical efficacy and safety of an additional core vitrectomy to the standard therapy in patients with exudative age-related macular degeneration (ARMD).

METHODS

In this prospective, controlled, single-centre study, 50 eyes of 50 patients (mean age: 74.1 ± 7.1; median 74 (69/78)) with ARMD were enrolled and randomized 1:1 to group 1 - core vitrectomy additional to three times injections of ranibizumab (3x Rbz) and Group 2 - 3x Rbz (control). 1 16 of 25 eyes in Group 1(64%) and 12 of 25 (48%) in Group 2 had a posterior vitreous detachment (PVD) prior to start of the study. Changes in best-corrected visual acuity (BCVA) using ETDRS charts, central macular thickness and macular volume (OCT) as well as the rate of reinjection with an OCT-based pro renata (PRN) protocol were monitored prospectively over 48 weeks. Forty-seven eyes completed follow-up at week 48.

RESULTS

In Group 1, 4 of 24 lost 1 line of BCVA (16.7%) and 3 of 24 lost 2 lines (12.5%), whereas 17 of 24 gained more than 1 line (70.8%) and improved in average by 9.8 letters. In Group 2, 3 of 23 remained stable and 20 of 23 gained more than or exactly 1 line (78.3%), resulting in 14.3 letters, with no loss of lines. Central macular thickness decreased by 85.58 μm (28.8%) in Group 1 and by 121.43 μm (32.68%) in Group 2 compared with baseline. In Group 1, four patients received three additional and two patients, two additional Rbz injections. In Group 2, three patients received three additional, three patients two and 12 patients one additional Rbz injections. This yielded in an average injection rate of 3.66 in Group 1 and 4.17 in Group 2 over 48 weeks. Posterior vitreous detachment (PVD) was identified in Group 1 in 16 of 24 (66.7%) and in Group 2 in 12 of 23 (52.2%) patients at baseline. At week 48, 6 of 8 (75%) of the patients in Group 1 with initial attached vitreous showed a vitreal detachment, whereas only 1 of 11 (9%) in Group 2 had a new occurred detachment of the vitreous. No systemic or ocular adverse events were noticed.

CONCLUSION

An initial core vitrectomy combined with a conventional ranibizumab injection regimen for exudative AMD patients was safe and lead to similar functional results with less intravitreal ranibizumab injections over 48 weeks.

Intravitreal drug delivery in retinal disease: are we out of our depth?

INTRODUCTION

With the ever-increasing global burden of retinal disease, there is an urgent need to vastly improve formulation strategies that enhance posterior eye delivery of therapeutics. Despite intravitreal administration having demonstrated notable superiority over other routes in enhancing retinal drug availability, there still exist various significant physical/biochemical barriers preventing optimal drug delivery into the retina. A further complication lies with an inability to reliably translate laboratory-based retinal models into a clinical setting. Several formulation approaches have recently been evaluated to improve intravitreal therapeutic outcomes, and our aim in this review is to highlight strategies that hold the most promise.

AREAS COVERED

We discuss the complex barriers faced by the intravitreal route and examine how formulation strategies including implants, nanoparticulate carriers, viral vectors and sonotherapy have been utilized to attain both sustained delivery and enhanced penetration through to the retina. We conclude by highlighting the advances and limitations of current in vitro, ex vivo and in vivo retinal models in use by researchers globally.

EXPERT OPINION

Various nanoparticle compositions have demonstrated the ability to overcome the retinal barriers successfully; however, their utility is limited to the laboratory setting. Optimization of these formulations and the development of more robust experimental retinal models are necessary to translate success in the laboratory into clinically efficacious outcomes.

A metabolomic approach to animal vitreous humor topographical composition: a pilot study

The purpose of this study was to evaluate the feasibility of a (1)H-NMR-based metabolomic approach to explore the metabolomic signature of different topographical areas of vitreous humor (VH) in an animal model. Five ocular globes were enucleated from five goats and immediately frozen at -80 °C. Once frozen, three of them were sectioned, and four samples corresponding to four different VH areas were collected: the cortical, core, and basal, which was further divided into a superior and an inferior fraction. An additional two samples were collected that were representative of the whole vitreous body. (1)H-NMR spectra were acquired for twenty-three goat vitreous samples with the aim of characterizing the metabolomic signature of this biofluid and identifying whether any site-specific patterns were present. Multivariate statistical analysis (MVA) of the spectral data were carried out, including Principal Component Analysis (PCA), Hierarchical Cluster Analysis (HCA), and Partial Least Squares Discriminant Analysis (PLS-DA). A unique metabolomic signature belonging to each area was observed. The cortical area was characterized by lactate, glutamine, choline, and its derivatives, N-acetyl groups, creatine, and glycerol; the core area was characterized by glucose, acetate, and scyllo-inositol; and the basal area was characterized by branched-chain amino acids (BCAA), betaine, alanine, ascorbate, lysine, and myo-inositol. We propose a speculative approach on the topographic role of these molecules that are mainly responsible for metabolic differences among the as-identified areas. (1)H-NMR-based metabolomic analysis has shown to be an important tool for investigating the VH. In particular, this approach was able to assess in the samples here analyzed the presence of different functional areas on the basis of a different metabolite distribution.

Profile of ocriplasmin and its potential in the treatment of vitreomacular adhesion

The recent approval by the US Food and Drug Administration of ocriplasmin for the treatment of symptomatic vitreomacular adhesion (VMA), often associated with vitreomacular traction (VMT) and macular hole (MH), has brought new attention to the field of pharmacologic vitreolysis. The need for an enzyme to split the vitreomacular interface, which is formed by a strong adhesive interaction between the posterior vitreous cortex and the internal limiting membrane, historically stems from pediatric eye surgery. This review summarizes the different anatomic classifications of posterior vitreous detachment or anomalous posterior vitreous detachment and puts these in the context of clinical pathologies commonly observed in clinical practice of the vitreoretinal specialist, such as MH, VMT, age-related macular degeneration, and diabetic macular edema. We revisit the outcome of the Phase II studies that indicated ocriplasmin was a safe and effective treatment for selected cases of symptomatic VMA and MH. Release of VMA at day 28 was achieved by 26.5% of patients in the ocriplasmin group versus 10.1% in the placebo group (P<0.001). Interestingly, for MHs, the numbers were more remarkable. Predictive factors for successful ocriplasmin treatment were identified for VMT (VMA diameter smaller than 1,500 μm) and MH (smaller than 250 μm). In comparison with the highly predictable outcome after vitrectomy, the general success rate of ocriplasmin not under clinical trial conditions has not fully met expectations and needs to be proven in real-world clinical settings. The ocriplasmin data will be compared in the future with observational data on spontaneous VMA release, will help retina specialists make more accurate predictions, and will improve outcome rates.

In-depth mass spectrometric mapping of the human vitreous proteome

Mapping of proteins involved in normal eye functions is a prerequisite to identify pathological changes during eye disease processes. We therefore analysed the proteome of human vitreous by applying in-depth proteomic screening technologies. For ethical reasons human vitreous samples were obtained by vitrectomy from “surrogate normal patients” with epiretinal gliosis that is considered to constitute only negligible pathological vitreoretinal changes. We applied different protein prefractionation strategies including liquid phase isoelectric focussing, 1D SDS gel electrophoresis and a combination of both and compared the number of identified proteins obtained by the respective method. Liquid phase isoelectric focussing followed by SDS gel electrophoresis increased the number of identified proteins by a factor of five compared to the analysis of crude unseparated human vitreous. Depending on the prefractionation method proteins were subjected to trypsin digestion either in-gel or in solution and the resulting peptides were analysed on a UPLC system coupled online to an LTQ Orbitrap XL mass spectrometer. The obtained mass spectra were searched against the SwissProt database using the Mascot search engine. Bioinformatics tools were used to annotate known biological functions to the detected proteins. Following this strategy we examined the vitreous proteomes of three individuals and identified 1111 unique proteins. Besides structural, transport and binding proteins, we detected 261 proteins with known enzymatic activity, 51 proteases, 35 protease inhibitors, 35 members of complement and coagulation cascades, 15 peptide hormones, 5 growth factors, 11 cytokines, 47 receptors, 30 proteins of visual perception, 91 proteins involved in apoptosis regulation and 265 proteins with signalling activity. This highly complex mixture strikingly differs from the human plasma proteome. Thus human vitreous fluid seems to be a unique body fluid. 262 unique proteins were detected which are present in all three patient samples indicating that these might represent the constitutive protein pattern of human vitreous. The presented catalogue of human vitreous proteins will enhance our understanding of physiological processes in the eye and provides the groundwork for future studies on pathological vitreous proteome changes.

Oxidative responses induced by pharmacologic vitreolysis and/or long-term hyperoxia treatment in rat lenses

PURPOSE

The aim of the study was to investigate the protective effects of intact vitreous gel on the lens after pharmacologic vitreolysis and hyperoxia exposure in rats in vivo.

METHODS

Eyes of Sprague-Dawley rats were induced to posterior vitreous detachment (PVD) by pharmacologic vitreolysis, and the rats with and without PVD were treated with hyperoxia 3 h per day for 5 months. Lens transparency was monitored by a slit-lamp biomicroscope. A series of biochemical measurements were made in extracts of the lens cortex and nucleus. Ascorbate levels were measured in the aqueous and vitreous humors.

RESULTS

No significant differences in lens transparency or morphology were observed in all groups, and no significant biochemical changes were observed in the cortex or nucleus of lenses of the PVD group. In the lens nucleus, the values of water-soluble protein concentration in PVD + hyperoxia group were lower than that of the PVD group. The levels of water-soluble proteins, glutathione (GSH) and ascorbate decreased in the hyperoxia group with an intact vitreous body. Vitreolysis enhanced the effect of hyperoxia, decreasing soluble protein, GSH and ascorbate below the levels seen in eyes with vitreolysis alone. The levels of antioxidants and soluble proteins were lower in the lens nucleus, and the effects of vitreolysis plus hyperoxia were more significant in the nucleus. Hyperoxia and hyperoxia plus vitreolysis reduced catalase activity and increased oxidized GSH to a greater extent in the lens cortex, although these treatments increased protein-GSH mixed disulfides in both regions. Long-term hyperoxia also lowered ascorbate levels in the vitreous and aqueous humors, an effect that was enhanced by vitreolysis.

CONCLUSIONS

Exposure to excess molecular oxygen produces significant oxidative damage to the lens, especially the lens nucleus. These effects were enhanced by pharmacologic vitreolysis, indicating that intact vitreous gel protects the lens from oxidative damage.

Environmental light and endogenous antioxidants as the main determinants of non-cancer ocular diseases

The human eye is constantly exposed to sunlight and artificial lighting. Exogenous sources of reactive oxygen species (ROS) such as UV light, visible light, ionizing radiation, chemotherapeutics, and environmental toxins contribute to oxidative damage in ocular tissues. Long-term exposure to these insults places the aging eye at considerable risk for pathological consequences of oxidative stress. Furthermore, in eye tissues, mitochondria are an important endogenous source of ROS. Over time, all ocular structures, from the tear film to the retina, undergo oxidative stress, and therefore, the antioxidant defenses of each tissue assume the role of a safeguard against degenerative ocular pathologies. The ocular surface and cornea protect the other ocular tissues and are significantly exposed to oxidative stress of environmental origin. Overwhelming of antioxidant defenses in these tissues clinically manifests as pathologies including pterygium, corneal dystrophies, and endothelial Fuch's dystrophy. The crystalline lens is highly susceptible to oxidative damage in aging because its cells and their intracellular proteins are not turned over or replaced, thus providing the basis for cataractogenesis. The trabecular meshwork, which is the anterior chamber tissue devoted to aqueous humor drainage, has a particular susceptibility to mitochondrial oxidative injury that affects its endothelium and leads to an intraocular pressure increase that marks the beginning of glaucoma. Photo-oxidative stress can cause acute or chronic retinal damage. The pathogenesis of age-related macular degeneration involves oxidative stress and death of the retinal pigment epithelium followed by death of the overlying photoreceptors. Accordingly, converging evidence indicates that mutagenic mechanisms of environmental and endogenous sources play a fundamental pathogenic role in degenerative eye diseases.

Vitreous surgery impact in glaucoma development in liver transplanted familial amyloidosis ATTR V30M Portuguese patients

PURPOSE

Familial amyloidosis with polyneuropathy (FAP) sometimes courses with vitreous amyloid. The aim of this study was to evaluate the incidence of glaucoma after vitrectomy in FAP patients.

METHODS

A total of 79 eyes of 42 liver transplanted FAP patients and 16 eyes of 16 non-FAP patients with rhegmatogenous retina detachment were collected. The patients were divided in to three groups: Group I - FAP patients with vitreous opacities submitted to vitrectomy, Group II - FAP patients without vitreous opacities and not submitted to vitrectomy and, Group III - non-FAP patients with rhegmatogenous retinal detachment submitted to vitrectomy. The Group I was subdivided into: Ia - "complete" vitrectomy; Ib - "incomplete" vitrectomy. The onset of glaucoma was considered when the intraocular pressure level was higher than 21 mmHg, with concomitant visual field abnormalities and optic nerve cupping.

RESULTS

Post vitrectomy glaucoma was more frequent in Group I (56.1%) than in Group III (12.5%) and in Group II (10.5%). We observed a higher incidence of glaucoma in the Ia than in the Ib subgroup (86.4 vs. 21.1%) and earlier appearance in subgroup Ia (7.9 ± 3.6 vs. 39.5 ± 6.6 months).

CONCLUSION

Vitrectomy induced the development of glaucoma in FAP patients.

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.

Vitreous substitutes: a comprehensive review

Vitreoretinal disorders constitute a significant portion of treatable ocular disease. Advances in vitreoretinal surgery have included the development and characterization of suitable substitutes for the vitreous. Air, balanced salt solutions, perfluorocarbons, expansile gases, and silicone oil serve integral roles in modern vitreoretinal surgery. Vitreous substitutes vary widely in their properties, serve different clinical functions, and present different shortcomings. Permanent vitreous replacement has been attempted with collagen, hyaluronic acid, hydroxypropylmethylcellulose, and natural hydrogel polymers. None, however, have proven to be clinically viable. A long-term vitreous substitute remains to be found, and recent research suggests promise in the area of synthetic polymers. Here we review the currently available vitreous substitutes, as well those in the experimental phase. We classify these compounds based on their functionality, composition, and properties. We also discuss the clinical use, advantages, and shortcomings of the various substitutes. In addition we define the ideal vitreous substitute and highlight the need for a permanent substitute with long-term viability and compatibility. Finally, we attempt to define the future role of biomaterials research and the various functions they may serve in the area of vitreous substitutes.

Towards an ideal biomaterial for vitreous replacement: Historical overview and future trends

Removal of the natural vitreous body from the eye and its substitution with a tamponade agent may be necessary in cases of complicated retinal detachment. Many materials have been variously proposed and tested over the years in an attempt to find an ideal vitreous substitute. This review highlights the evolution of research in the field of vitreous replacement and chronicles the main advances that have been made in such a context. The suitability and limitations of vitreous tamponade agents and substitutes in current clinical use are examined, and the future promise of experimentally tested biomaterials are described and discussed. Future trends in research are also considered and, specifically, the great potential of polymeric hydrogels is emphasized, as they seem to be very effective in closely mimicking the features of the natural vitreous and they could successfully act as long-term vitreous substitutes without inducing clinical complications in the patient's eye.

Oxygen distribution in the human eye: relevance to the etiology of open-angle glaucoma after vitrectomy

PURPOSE

Vitrectomy, when followed by cataract surgery, increases the risk of open-angle glaucoma. This study was conducted in patients to determine whether these procedures are associated with increased exposure of the trabecular meshwork to oxygen.

METHODS

Oxygen distribution was recorded with a fiberoptic probe in patients undergoing surgery for cataract, glaucoma, or retinal disease. pO(2) was measured beneath the central cornea, in the mid-anterior chamber, and in the anterior chamber angle. In patients who were pseudophakic or were scheduled for cataract extraction, pO(2) was also measured in the posterior chamber and near the lens.

RESULTS

Eyes with no previous cataract or vitrectomy surgery had steep oxygen gradients in the aqueous humor between the cornea and lens. pO(2) was low in the posterior chamber and near the lens. Previous vitrectomy was associated with significantly increased pO(2) in the posterior chamber. Eyes with previous cataract surgery had significantly elevated pO(2) only in the posterior chamber and in front of the intraocular lens (IOL). Eyes that had both vitrectomy and previous cataract surgery had increased pO(2) in the posterior chamber, anterior to the IOL, and in the anterior chamber angle. pO(2) in the posterior chamber and the anterior chamber angle correlated strongly.

CONCLUSIONS

Oxygen metabolism by the lens and cornea establishes oxygen gradients in the anterior segment. Vitrectomy and cataract surgery increase pO(2) in the anterior chamber angle, potentially damaging trabecular meshwork cells. We propose that oxygen levels in the anterior chamber angle are strongly influenced by oxygen derived from the ciliary body circulation.

The alpha-receptor for platelet-derived growth factor confers bone-metastatic potential to prostate cancer cells by ligand- and dimerization-independent mechanisms

Prostate adenocarcinoma is the second leading cause of cancer death among men, due primarily to the fact that the majority of prostate cancers will eventually spread to the skeleton. Metastatic dissemination requires a complex series of coordinated events that result in cells that escape from the primary tumor into the circulation and eventually colonize a distant organ. The ability of these cells to evolve into macroscopic metastases depends strongly on their compatibility with, and ability to utilize, this new microenvironment. We previously showed that bone-metastatic prostate cancer cells exposed to human bone marrow respond by activation of cell survival pathways, such as phosphoinositide 3-kinase/Akt, and that these events are mediated by the alpha-receptor for platelet-derived growth factor (PDGFRalpha). Our studies and others have shown that PDGFRalpha may be activated by mechanisms independent of PDGF ligand binding. Here, we provide conclusive evidence that soluble components of human bone marrow can activate PDGFRalpha through a mechanism that does not require the canonical binding of PDGF ligand(s) to the receptor. In particular, we found that dimerization of PDGFRalpha monomers is not induced by human bone marrow, but this does not prevent receptor phosphorylation and downstream signaling from occurring. To establish the relevance of this phenomenon in vivo, we used a PDGFRalpha mutant lacking the extracellular ligand-binding domain. Our studies show that this truncated PDGFRalpha is able to restore bone-metastatic potential of prostate cancer cells as effectively as the full-length form of the receptor.