Photoreceptors Repair By Autologous Transplantation Of Retinal Pigment Epithelium And Partial-thickness Choroid Graft In Rabbits

Background:Age-related macular degeneration (AMD) is the leading cause of severe central visual acuity loss in one or both eyes in people over 50 years of age in western countries, and the third most common cause of visual impairment in the elderly Chinese population in Taiwan, which represents an atrophic or exudative form. In atrophic AMD, geographic atrophy of the retinal pigment epithelium (RPE) and the overlying photoreceptors loss lead to a decrease visual acuity. In exudative AMD, the new vessels arising from choriocapillaris disrupt and destroy the normal architecture of the photoreceptors, the RPE, the bruch's membrane, and the choriocapillaris, and remaining outer retina leading to the formation of a disciform scar. Although whether the initial pathological changes emerge in RPE or the choriocapillaris is still unknown, it is certain that visual loss typically results from photoreceptor dysfunction due to underling atrophy or choroidal neovascularization (CNV).Although photodynamic therapy (PDT) and antiangiogenic approaches have effectiveness in treating early stage of exudative AMD, they have not poven effective in more complicated subtypes of membranes, such as subretinal hemorrhage and disciform scar. Therefore, surgical strategies aim to reconstitute functioning RPE. Purpose:To create a RPE debridement animal model and observe the histopathological changes. To investigate whether autologous retinal pigment epithelium (RPE) and partial-thickness choroid graft can revascularize on atrophy choriocapillaries and repair degenerative photoreceptors overlying the mechanically damaged bruch's membrane.Methods:Part I Histopathological changes after RPE debridements.Abrasive debridement of RPE was performed with a metal cannula after superior retinal bleb detachments in rabbits. Animals were examined by Fundus Fluorescein Angiography(FFA)and Indocyanine Green Angiography(ICGA)in seriate 7 days, 15days, 1 month and 3 months post-debridements. and tissue sections were evaluated using light microscope and transmission electron microscope at corresponding time points.Part II Histological evidence for revascularization of an autologous retinal pigment epithelium and partial-thickness choroid graftAutologous RPE and part-thickness choroid graft was prepared beneath the inferior retina and was transplanted to the debridement area 14 days after debreidments. Animals were examined by FFA and ICGA in seriate 7 days, 1 month and 3 months post-transplantation respectively. Tissue sections were evaluated using light microscope and transmission electron microscope at corresponding time points.Part III Photoreceptors repair by autologous transplantation of retinal pigment epithelium and partial-thickness choroid graft. Autologous RPE and part-thickness choroid graft was prepared beneath the inferior retina and was transplanted to the debridement area 14 days after debreidments.The debridement-only sites served as control. Animals were examined by light microscope and transmission electron microscope in seriate 7 days, 1 month and 3 months post-transplantation and according time points post-debridement respectively. Tissue sections were evaluated using light microscope and transmission electron microscope at corresponding time points.Results:1. The debrided area was not completely resurfaced by surrounding elongated RPE cells, the choriocapillaries beneath the debrided area underwent degeneration, and the photoreceptors overlying the debrided area show gradually degeneration and loss.2. All grafts were revascularization from 7days to 3 months after transplantion. The vasculature was opened and perfused.3. When analyzed at 7 days post-transplantation, short buds of inner segment were observed. The outer segments (OS) were of insufficient length to be observed, but by 1 and 3 months, a significant elongation of OS was detected. In control retinas from 21 days (the same time point as 7days post-transplantation) to 3 months post-RPE debridement, the outer nuclear layer cells were gradually irregularly organized and reduced.Conclusions:The type of abrasive debridement has been suggested as a model of therapy for macular degeneration as there exists a high correlation between RPE dropout, choriocapillaries atrophy and loss of photoreceptors function. Moreover, the bruch's membrane was mechanically damaged, however, not broken through, which resembles the pathology after CNV excision. Therefore, the histological changes in the debridement-only sites are partial evidence to the condition that the patients experienced little visual improvement, and even worsen following CNV excision. And the results in graft-transplantation group have shown that autologous RPE and partial-thickness choroid transplantation have the capacity to repair the outer segment regeneration in degenerative photoreceptors.