Vascular endothelial growth factor (VEGF) is the major angiogenic factor in PDR that promotes neovascularization and vascular leakage [2]. The angiogenic switch involves in part the proteolytic degradation of basement membranes and ECM components by matrix metalloproteinases (MMPs). (r=0.845; P<0.001) and MMP-9 (r=0.775; p<0.001), and between RX-3117 levels of MMP-1 and MMP-9 (r=0.857; p<0.001). In epiretinal membranes, cytoplasmic immunoreactivity for MMP-9 was present in vascular endothelial cells and stromal monocytes/macrophages and neutrophils. Our findings suggest that among the MMPs measured, MMP-1 and MMP-9 may contribute to the angiogenic switch in PDR. == Introduction == Proliferative diabetic retinopathy (PDR), a long-term complication of diabetes, is characterized by vasculopathy associated with abnormal angiogenesis and expansion of extracellular matrix (ECM) resulting in the outgrowth of fibrovascular membranes at the vitreoretinal interface. Formation of fibrovascular tissue results in severe complications such as vitreous hemorrhage and traction retinal detachment. Angiogenesis, the sprouting of new blood vessels from preexisting blood vessels, is a multistep process requiring the degradation of the basement membranes and ECM, endothelial cell migration, endothelial cell proliferation, Rabbit Polyclonal to EPN1 and capillary tube formation [1]. Vascular endothelial growth factor (VEGF) is the major angiogenic factor in PDR that promotes neovascularization and vascular leakage [2]. The angiogenic switch involves in part the proteolytic degradation of basement membranes and ECM components by matrix metalloproteinases (MMPs). In addition to removing the physical barriers to new vessel growth, MMPs proteolytically release VEGF from the ECM-associated reservoirs [3,4], resulting in increased VEGF bioavailability and triggering the VEGF-driven angiogenic switch [3,4]. MMPs are a family of zinc ion-binding Ca2+-dependent neutral endopeptidases that act together or in concert with other enzymes to degrade most components of the ECM. At least 25 MMP members have been indentified and are divided into collagenases (MMP-1, MMP-8, and MMP-13), gelatinases (MMP-2, and MMP-9), stromelysins RX-3117 (MMP-3, MMP-10, and MMP-11), matrilysins (MMP-7, and MMP-26), membrane-type MMPs, and others [5]. Most of the MMPs are inhibited by specific endogenous tissue inhibitors which are known as tissue inhibitors of matrix metalloproteinases (TIMPs) [5]. Under steady state physiologic conditions, the expression of MMPs in most tissues is relatively low, with the possible exception of MMP-2, which RX-3117 appears to be expressed constitutively [1]. These enzymes have been implicated in invasive cell behavior and recent studies have indicated that MMPs are generally up-regulated in several conditions that accompany angiogenesis and play an important role in the initiation of angiogenesis [1]. In PDR, the levels of certain MMPs are increased dramatically [6-9]. This up-regulation of MMPs is linked to angiogenesis and progression of PDR. However, the relative relevance of individual MMPs to angiogenesis associated with PDR remains to be elucidated. To develop efficient specific inhibitors for anti-angiogenic therapy, it is necessary to know which MMPs are more likely to be involved in the angiogenic process in PDR. Therefore, we measured the levels of the MMPs MMP-1, MMP-2, MMP-3, MMP-7, MMP-9, and MMP-13 in the vitreous fluid from patients with PDR and nondiabetic patients and correlated their levels with the levels of the angiogenic factor VEGF. The association of MMPs with VEGF is likely to be an indicator of the relevance of MMPs to angiogenesis and diabetic retinopathy. == Materials and Methods == == Ethics statement == The study was conducted according to the tenets of the Declaration of Helsinki. All the patients were candidates for vitrectomy as a surgical procedure. All patients signed a preoperative informed written consent and approved the use of the excised epiretinal membranes and vitreous fluid for further analysis and clinical research. The study design and the protocol was approved by the Research Centre and Institutional Review Board of the College of Medicine, King Saud University. The sections from the control patients were obtained from patients treated at the University Hospital, University of Leuven, Belgium, in full compliance with tenets of the Declaration of Helsinki. We used archived material and patients gave written consent at admission for the use of the leftover material in studies. The Ethics Committee.