Boris V. Stanzel

TRANSPLANTATION OF THE RPE IN AMD

The retinal pigment epithelium (RPE) maintains retinal function as the metabolic gatekeeper between photoreceptors (PRs) and the choriocapillaries. The RPE and Bruchs membrane (BM) suffer cumulative damage over lifetime, which is thought to induce age-related macular degeneration (AMD) in susceptible individuals. Unlike palliative pharmacologic treatments, replacement of the RPE has a curative potential for AMD. This article reviews mechanisms leading to RPE dysfunction in aging and AMD, laboratory studies on RPE transplantation, and surgical techniques used in AMD patients. Future strategies using ex vivo steps prior to transplantation, BM prosthetics, and stem cell applications are discussed. The functional peculiarity of the macular region, epigenetic phenomena leading to an age-related shift in protein expression, along with the accumulation of lipofuscin may affect the metabolism in the central RPE. Thickening of BM with age decreases its hydraulic conductivity. Drusen are deposits of extracellular material and formed in part by activation of the alternative complement pathway in individuals carrying a mutant allele of complement factor H. AMD likely represents an umbrella term for a disease entity with multifactorial etiology and manifestations. Presently, a slow progressing (dry) non-neovascular atrophic form and a rapidly blinding neovascular (wet) form are discerned. No therapy is currently available for the former, while RPE transplantation and promising (albeit non-causal) anti-angiogenic therapies are available for the latter. The potential of RPE transplantation was demonstrated in animal models. Rejection of allogeneic homologous transplants in patients focused further studies on autologous sources. In vitro studies elucidated cell adhesion and wound healing mechanisms on aged human BM. Currently, autologous RPE, harvested from the midperiphery, is being transplanted as a cell suspension or a patch of RPE and choroid in AMD patients. These techniques have been evaluated from several groups. Autologous RPE transplants may have the disadvantage of carrying the same genetic information that may have led to AMD manifestation. An intermittent culturing step would allow for in vitro therapy of the RPE, its rejuvenation and prosthesis of BM to improve the success RPE transplants. Recent advances in stem cell biology when combined with lessons learned from studies of RPE transplantation are intriguing future therapeutic modalities for AMD patients.

Healing of Retinal Photocoagulation Lesions

PURPOSE To systematically assess the changes in retinal morphology during the healing of retinal photocoagulation lesions of various clinical grades. METHODS Rabbits were irradiated with a 532-nm Nd:YAG laser with a beam diameter of 330 microm at the retinal surface, a power of 175 mW, and pulse durations between 5 and 100 ms. Retinal lesions were clinically graded 1 minute after placement as invisible, barely visible, light, moderate, intense, very intense, and rupture and were assessed histologically at six time points from 1 hour to 4 months. RESULTS At all pulse durations, the width of the retinal lesions decreased over time. At clinical grades of light and more severe (pulse durations, 10-100 ms), retinal scarring stabilized at 1 month at approximately 35% of the initial lesion diameter. Lesions clinically categorized as barely visible and invisible (pulse durations of 7 and 5 ms) exhibited coagulation of the photoreceptor layer but did not result in permanent scarring. In these lesions, photoreceptors completely filled in the damaged areas by 4 months. CONCLUSIONS The decreasing width of the retinal damage zone suggests that photoreceptors migrating from unaffected areas fill in the gap in the photoreceptor layer. Laser photocoagulation parameters can be specified to avoid not only the inner retinal damage, but also permanent disorganization and scarring in the photoreceptor layer. These data may facilitate studies to determine those aspects of laser treatment necessary for beneficial clinical response and those that result in extraneous retinal damage.

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

Summary 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.

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.

Enhancement of retinal pigment epithelial culture characteristics and subretinal space tolerance of scaffolds with 200 nm fiber topography

Tissue engineered retinal pigment epithelial (RPE) transplantation is a promising cell-based therapy for age-related macular degeneration. The aim of this work is to develop a supportive scaffold with a favorable topography to aid functional RPE monolayer maintenance while being tolerated underneath the retina. To this end, films and electrospun substrates with fiber diameters ranging from 200 to 1000 nm were made of polyethylene terephthalate or poly(L-lactide-co-ε-caprolactone), and then tested using human fetal RPE cells in vitro and transplanted subretinally in rabbits. The results indicated that RPE on both 200 nm fiber variants showed the highest cell densities, adherent monolayers achieved deeper pigmentation, and more uniform hexagonal tight junctions. Facile subretinal implantation of flat 200 nm fiber membranes was achieved by electrospinning them onto a porous rigid-elastic carrier. Spectral-domain optical coherence tomography showed a reattached, slightly thinned retina overlying the implants over 2 weeks observation. Histology demonstrated native RPE variably migrated onto the nanofibers, and a reactive gliosis with some photoreceptor degeneration. In conclusion, scaffolds with 200 nm fiber topography enhanced RPE culture, showed subretinal biocompatibility, and should thus be considered for future cell-based therapies in blinding retinal diseases.

Release And Velocity Of Micronized Dexamethasone Implants With An Intravitreal Drug Delivery System: Kinematic Analysis With a High-speed Camera

Purpose: Ozurdex, a novel dexamethasone (DEX) implant, is released by a drug delivery system into the vitreous cavity. We analyzed the mechanical release aperture of the novel applicator, obtained real-time recordings using a high-speed camera system and performed kinematic analysis of the DEX application. Design: Experimental study. Methods: The application of intravitreal DEX implants (6 mm length, 0.46 mm diameter; 700 &mgr;g DEX mass, 0.0012 g total implant mass) was recorded by a high-speed camera (500 frames per second) in water (Group A: n = 7) or vitreous (Group B: n = 7) filled tanks. Kinematic analysis calculated the initial muzzle velocity as well as the impact on the retinal surface at approximately 15 mm of the injected drug delivery system implant in both groups. A series of drug delivery system implant positions was obtained and graphically plotted over time. Results: High-speed real-time recordings revealed that the entire movement of the DEX implant lasted between 28 milliseconds and 55 milliseconds in Group A and 1 millisecond and 7 milliseconds in Group B. The implants moved with a mean muzzle velocity of 820 ± 350 mm/s (±SD, range, 326–1,349 mm/s) in Group A and 817 ± 307 mm/s (±SD, range, 373–1,185 mm/s) in Group B. In both groups, the implant gradually decelerated because of drag force. With greater distances, the velocity of the DEX implant decreased exponentially to a complete stop at 13.9 mm to 24.7 mm in Group A and at 6.4 mm to 8.0 mm in Group B. Five DEX implants in Group A reached a total distance of more than 15 mm, and their calculated mean velocity at a retinal impact of 15 mm was 408 ± 145 mm/s (±SD, range, 322–667 mm/s), and the consecutive normalized energy was 0.55 ± 0.44 J/m2 (±SD). In Group B, none of the DEX implants reached a total distance of 6 mm or more. An accidental application at an angle of 30 grade and consecutively reduced distance of approximately 6 mm may result in a mean velocity of 844 and mean normalized energy of 0.15 J/m2 (SD ± 0.47) in a water-filled eye. Conclusion: The muzzle velocity of DEX implants is approximately 0.8 m/s and decreases exponentially over distance. The drag over time in vitreous is faster than in water. The calculated retinal impact energy does not reach reported damage levels for direct foreign bodies or other projectiles.

A Nanofibrillar Surface Promotes Superior Growth Characteristics in Cultured Human Retinal Pigment Epithelium

Background: To evaluate the influence of surface topography on the proliferation of the retinal pigment epithelium (RPE) by comparing nanofibrillar and smooth substrates. Methods: Electrospun polyamide nanofibers (EPN) are an engineered surface mimicking native basement membranes. Commonly used plastic (polystyrene, PS) and glass substrates have a smooth topography. All were analyzed by scanning electron microscopy. RPE cultures were established from fetal and adult donors. Growth curves were established on the above substrates. Cell cycle and growth fractions were analyzed with 5-ethynyl-2′-deoxyuridine (EdU) and 4′,6-diamidino-2-phenylindole (DAPI). Results: At a magnification of ×5,000, EPN showed randomly overlapping fibers and pores. The surface of glass was slightly studded yet regular, in contrast to ideally smooth PS. Polygonal cells grew on nanofibers in a colony-like distribution, while randomly spread spindle-shaped cell morphologies were seen on smooth surfaces. This was observed at all donor ages. Initial proliferation rates were higher on EPN, and similar final cell densities were reached in all age groups, compared to an age-related decline on PS. EdU/DAPI revealed faster cell cycles on EPN. Growth fractions were higher and maintained longer on EPN. Observed substrate differences in growth behavior were statistically significant. Conclusion: Surface topography appears to induce distinct RPE proliferation characteristics.

Ultrathin Polyimide Membrane as Cell Carrier for Subretinal Transplantation of Human Embryonic Stem Cell Derived Retinal Pigment Epithelium.

In this study, we investigated the suitability of ultrathin and porous polyimide (PI) membrane as a carrier for subretinal transplantation of human embryonic stem cell (hESC) -derived retinal pigment epithelial (RPE) cells in rabbits. The in vivo effects of hESC-RPE cells were analyzed by subretinal suspension injection into Royal College of Surgeons (RCS) rats. Rat eyes were analyzed with electroretinography (ERG) and histology. After analyzing the surface and permeability properties of PI, subretinal PI membrane transplantations with and without hESC-RPE were performed in rabbits. The rabbits were followed for three months and eyes analyzed with fundus photography, ERG, optical coherence tomography (OCT), and histology. Animals were immunosuppressed with cyclosporine the entire follow-up time. In dystrophic RCS rats, ERG and outer nuclear layer (ONL) thickness showed some rescue after hESC-RPE injection. Cells positive for human antigen were found in clusters under the retina 41 days post-injection but not anymore after 105 days. In rabbits, OCT showed good placement of the PI. However, there was loss of pigmentation on the hESC-RPE-PI over time. In the eyes with PI alone, no obvious signs of inflammation or retinal atrophy were observed. In the presence of hESC-RPE, mononuclear cell infiltration and retinal atrophy were observed around the membranes. The porous ultrathin PI membrane was well-tolerated in the subretinal space and is a promising scaffold for RPE transplantation. However, the rejection of the transplanted cells seems to be a major problem and the given immunosuppression was insufficient for reduction of xenograft induced inflammation.

Perspektive: Tissue engineering bei RPE-Transplantation in AMD

SummaryThe Retinal pigment epithelium (RPE) incurs a lifelong damage, which is one mechanism leading to age-related macular degeneration (AMD), the most common cause of blindness over 55. Despite intense research, to date the majority of those affected have no effective therapy available. Cell based replacement strategies of the RPE represent, in contrast to current pharmacologic interventions, a curative treatment. This article describes potential future perspectives of current autologous clinical RPE transplantation protocols. Intermittent culturing could potentially rejuvenate aged RPE. Age related changes of the RPE are reflected in culture, yet our findings suggest that they can be overcome with modern artificial substrates and defined culture media. Degenerations and surgical damage in Bruchs membrane may potentially compromise survival or function of transplanted RPE. Hence, an important adjunct to RPE replacement is Bruchs membrane prosthesis, for which we dedicated a significant proportion of this manuscript. Results of our in vitro and in vivo studies with amniotic membrane, porous polyester membranes and electrospun nanofibers are briefly summarized. We conclude with an outlook on future research on the use of tissue engineering for replacement of the entire RPE/Choriocapillaris Complex, and on promising results from stem cell derived RPE-like cells.ZusammenfassungEin lebenslang kumulierender Schaden am Retinalen Pigment Epithel (RPE) bedingt unter anderem die altersbedingte Makula Degeneration, die häufigste Erblindungsursache ab 55. Trotz intensiver Forschung, gibt es bis heute für den Großteil der Betroffenen keine effektive Therapie. Zell basierte Ersatz Strategien des RPE stellen, im Gegensatz zu derzeitigen pharmakologischen Interventionen, eine kurative Therapieoption dar. Dieser Artikel behandelt mögliche Zukunfts-Perspektiven von mittlerweile klinisch praktizierten autologen RPE Transplantations-Protokollen. Durch zwischenzeitliche Zell Kultur könnte man eine Verjüngung der Zellen erreichen. Obwohl altersbedingte Veränderungen der RPE Zelle auch für die Kultur ein Hindernis sind, fanden wir dass dies mit modernen Zellkultur Substraten und definierten Kulturmedien möglicherweise überwindbar ist. Degenerationen und chirurgisches Trauma der Bruchschen Membran verhindern möglicherweise überleben und/oder Transplantat Funktion. Ein wesentlicher Aspekt des RPE Ersatz ist somit auch ein prothetischer Ersatz der Bruchschen Membran, wofür ein wesentlicher Teil dieses Artikels gewidmet wurde. Wir stellen zusammenfassend Erkenntnisse aus Untersuchungen mit Amnion Membran, porösen synthetischen Polyestern, sowie elektrogesponnenen Nanofasern vor. Abschließend wird die Bedeutung dieser Ergebnisse für zukünftige Forschungsziele, wie der Einsatz von Tissue engineering für Rekonstruktion des gesamten RPE/Choriocapillaris Komplex sowie hoffnungsreiche Daten über aus Stammzellen in vitro differenzierte RPE ähnliche Zellen diskutiert.

Longterm cultures of the aged human RPE do not maintain epithelial morphology and high transepithelial resistance

Dear Editor, Visual rehabilitation achieved with peripheral RPE autografts in exudative AMD is only modest. Moreover, complication rates using the popular RPE–choroid patch technique remain relatively high. Tissue-engineered transplants might improve the outcome of RPE transplantation. A culturing step could place cells on a substrate prior to transplantation, thereby optimizing delivery and long-term function [1]. This would require sufficient cellular plasticity (i.e., response to environmental stimuli) to achieve a well-differentiated, functional graft. While culture plasticity was confirmed for fetal cells or RPE cell lines [2, 3], only sparse information is available for aged RPE [4]. We studied the influence of culture conditions on select differentiation characteristics in long-term primary RPE cultures from ten human donors above age 55, and compared them to a 23-year-old and two fetal donors (20 and 21 weeks of gestation respectively). The main outcome measures at 6 weeks post-confluence (PC) were morphology and transepithelial resistance (TER), an electrophysiological method for assessing tight junctions build-up. Eyes were preserved within 6 hours of death. Adult primary RPE cultures (aRPE) were initiated from: (1) mechanically scraped RPE, or (2) collagenase pretreated (1 mg/ml for 40 minutes, CLS I, Worthington Biochemical Corp, Lakewood, NJ, USA) and mechanically scraped RPE, or (3) fetal (fRPE) and adult cultures started from floater passages [2]. Cells were grown on permeable polyester inserts (Transwells, Corning Inc., Corning, NY, USA) in modified Hu & Bok media [2], containing 2% calf serum, basic FGF (5 ng/ml), L-alanyl-L-glutamine (2 mM), Albumax (200 μg/ml), and antibiotics/antimycotics. RPE culture purity was confirmed by a uniform pancytokeratin staining. Experimental matrices analyzed the influence of above harvesting methods, seeding density, laminin coating (2 μg/cm), and media composition (2% vs 10% serum until confluence, or calcium switch at confluence, or 5 mM vs 25 mM glucose) on above outcome measures. Morphology was monitored weekly in all and transepithelial resistance (TER) in all conditions, except the laminin matrix (i.e., seven of ten aged donors). Presented in part at the annual meeting of the Association for Research in Vision and Ophthalmology, Fort Lauderdale, FL, USA, April 30–May 4 2006.