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Effects of Low Molecular-Weight Heparin on the Epiretinal Membranes in Proliferative Vitreoretinopathy. A New Approach for PVR Prophylaxis?

1Vidinova C., 2Vidinov N., 1Kohler K., 3Gougoutchkova P.,
1Eberhard-Karls-Universität Tübingen, Universitäts-Augenklinik, Forschungsstelle für experimentelle Ophthalmology (Tübingen)
2Medical University Sofia, Department of Anatomy and Histology, Eye Anatomy (Sofia)
3Medical University Sofia, Department of Ophthalmology, Vitro-retinal Clinic (Sofia)

Purpose: To find new therapeutic concepts in the prophylaxis of PVR membrane formation, by using a low molecular weight heparin (LMWH), a pharmaceutical agent with reduced side effects and high bioactivity, interacting with the proteoglycan network of the extracellular matrix. In this study, we examined the ultrastructural and immunohistochemical characteristics of the PVR membranes under the influence of LMWH.
Method: We used epiretinal membranes, taken during vitrectomy from patients with PVR stage C2. Cell cultures were made from the received membranes and LMWH was added to the culture medium in half of the samples. The other half served as untreated control. After ten days in culture, membranes were examined with standard techniques for transmission and scanning electron microscopy, histochemically with Safranin O and immunohistochemically with antibodies against Vimentin and GFAP(glial fibrillary acidic protein).
Results: Fibroblast-like and epitheloid–like cells were observed in the epiretinal membranes of the control group. The cells were connected to each other with tight intercellular junctions (zonulae occludens). In the extracellular matrix collagen fibres and a great number of proteoglycan complexes were observed. The membranes stained positively for Vimentin and GFAP. The heparin treated membranes were mainly comprised of fibroblast-like, fusiform- shaped cells, that stained immunohistochemically in the same way for Vimentin and GFAP. However, cell to cell connections were totally disrupted and in some places even missing. A great number of cells showed marks of degeneration: pycnotic nuclei, distorted mitochondria complexes, shrinked plasmalema. The proteoglycans in the extracellular matrix were diminished in number. In the matrix the collagen fibres begin to stick to each other due to the lack of proteoglycan bridges in between. Furthermore some of the fibres start losing their cross-striation, which is a mark of degeneration.
Conclusions: LMWH induces changes in the type and number of proteoglycan complexes in the extracellular matrix of the examined structures. In this way it causes matrix disorganisation, disruptions in cell to cell contacts, and in collagen-proteoglycan bindings. Furthermore it hinders the processes of cell proliferation, membrane stabilisation and maturation. In this way it lowers the possibilities for further membrane development. It is therefore tempting to expect that LMWH therapy during vitrectomy surgery might be successful in the prophylacxis of further membrane formation in PVR patients.