A novel role for coagulation proteins in the development of proliferative vitreoretinopathy

Abstract In patients with retinal detachment, the major cause of recurrent redetachment is proliferative vitreoretinopathy (PVR, 5-10 %). PVR is characterized by the formation of fibrotic contractile membranes on either side of the retina, causing the retina to detach. The retinal pigment epithelium (RPE) has an important role in the homeostasis and functioning of the retina and forms the outer blood-retinal barrier by separating the retina from the blood vessels in the choroid. Coagulation proteins may come in contact with the RPE due to hemorrhage or breakdown of the blood-retinal barrier. We were the first to demonstrate that vitreous of patients with established PVR contains elevated levels of thrombin. Intravitreal thrombin (and to some extent factor Xa) can induce the release of a broad panel of cytokines, chemokines and growth factors by RPE which regulate local inflammatory and fibrotic responses, fitting PVR pathogenesis. These responses include the differentiation of monocytes into macrophages and that of RPE into myofibroblasts. Both cell types are abundantly present in fibrotic retinal membranes. The clinically available direct thrombin-inhibitor Dabigatran is able to inhibit the thrombin-induced release of cytokines, chemokines and growth factors and may thus be an interesting therapy for PVR development and other vitreoretinal disorders which are characterized by breakdown of the blood-retinal barrier. Currently, in the Rotterdam Eye Hospital, it has been found that Dabigatran reaches the eye in a potential effective concentration and a clinical trial with Dabigatran is planned with patients at risk for developing PVR

Thrombin Generation in Vitreous and Subretinal Fluid of Patients with Retinal Detachment

Purpose: To measure prothrombin fragments (F1+2) and thrombin-antithrombin complex (TAT) in vitreous and subretinal fluid (SRF) of rhegmatogenous retinal detachment (RRD) patients and to validate and further specify our earlier finding of increased thrombin activity in patients with proliferative vitreoretinopathy (PVR). Methods: F1+2 and TAT were measured in 31 vitreous and 16 SRF samples using the Enzygnost® immunoassays. Results: We found significant levels of F1+2 and TAT in the vitreous of all patients with RRD compared to patients with macular hole or macular pucker. However, there was no significant difference between patients who would develop PVR in the future, had established PVR, and patients with uncomplicated RRD both in vitreous concentrations of F1+2 (Kruskal-Wallis p = 0.963) and TAT (p = 0.516). Conclusion: The analysis of F1+2 and TAT confirmed significant thrombin generation in both vitreous and SRF of patients with RRD. An imbalance between the thrombin regulation mechanisms TAT and α2-macroglobulin possibly explains the difference from our previous findings

The Role of Thrombin in Proliferative Vitreoretinopathy

PURPOSE. To determine the role of thrombin in the development of proliferative vitreoretinopathy (PVR). METHODS. Vitreous was collected from patients undergoing a vitrectomy (macular holes and puckers, n ¼ 11 [controls]; retinal detachment without PVR development following vitrectomy, n ¼ 15 [RRD1]; retinal detachment with PVR development within 6 months after vitrectomy, n ¼ 11 [RRD2]; and established PVR, n ¼ 14 [PVR]). Thrombin activity in vitreous was determined using a thrombin-specific chromogenic substrate. ARPE-19 cells were stimulated with 83 diluted vitreous samples in the presence and absence of hirudin. The samples were analyzed at t ¼ 0 and t ¼ 24 hours for the presence of 27 cytokines/ chemokines and growth factors using a multiplex approach. In comparable studies, ARPE-19 cells were stimulated for 2 hours, and mRNA expression levels for CCL2, CXCL8, GMCSF, IL6, and PDGFB were determined by real-time quantitative (RQ)-PCR. RESULTS. Thrombin activity was significantly (P < 0.05) higher in vitreous of the PVR group compared to the other groups. Proliferative vitreoretinopathy vitreous stimulated the production of chemokine (C-C motif) ligand (CCL)2, chemokine (C-X-C motif) ligand (CXCL)8, granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-6, and plateletderived growth factor (PDGF)-BB by ARPE-19 to significantly (P < 0.05) higher levels than vitreous from the RRD1 and RRD2 groups. These effects of PVR vitreous were significantly (P < 0.05) reduced by hirudin. These data were confirmed by mRNA studies. CONCLUSIONS. Thrombin activity is increased in vitreous of patients with established PVR and is involved in the activation of proinflammatory and profibrotic pathways in RPE cells. Inhibition of thrombin activity may therefore represent a potential treatment option for proliferative vitreoretinopathy

Cranial palaeopathologies in a Late Cretaceous mosasaur from the Netherlands

Here we describe multiple pathological skeletal elements in a specimen assigned to a globidensine mosasaur as Prognathodon cf. sectorius. This individual, NHMM 2012 072, was recovered from the upper Lixhe 3 Member (Gulpen Formation, upper Maastrichtian) near Maastricht, the Netherlands. In all likelihood, it was bitten in the snout by a large, possibly conspecific mosasaur – and survived this attack. The specimen described here is among the very few with clear and unambiguous evidence of (very likely intraspecific) agonistic interactions amongst mosasaurs. Despite significant injuries, including partial amputation of the premaxilla, this animal initially recuperated from the encounter, but the subsequent infectious processes as a result of this attack were still ongoing at the time of death. Radiological and morphological features suggest chronic osteomyelitis which led to loss of bone within the left maxilla, which probably hampered the ability to feed, potentially contributing to its demise. This case study illustrates the potential of integrative three-dimensional approaches in palaeopathological studies to provide a much more comprehensive and detailed description of alterations and underlying physiological processes

A novel flamelet-based model for 3D DNS of Mild combustion with CH₄/H₂ fuels

MILD combustion, also known as Flameless combustion, is a relatively new combustion concept which has a unique potential in enhancement of efficiency and reduction of emissions, in particular NOx. Very recently, the idea of using alternative fuels such as Syngas in MILD combustion has been emerged as a very clean combustion technology which has notable environmental and economic advantages. Exploitation ofMILD/Syngas combustion in industrial applications has been largely hindered by the lack of knowledge in complex processes associated with its stabilization. The stabilization mechanism of MILD combustion is mainly based on autoignition and presence of H2 introduces preferential diffusion effects. In this study, we conduct 3D DNS of MILD combustion with CH4/H2 fuels using detailed chemistry and transport models in order to obtain a better understanding of autoignition and preferential differential effects in MILD/Syngas combustion condition. A reduced flamelet-based chemistry model is developed to include these effects using Igniting Mixing Layer (IML) Flamelets. This model shows a considerable improvement compared to the commonly-used Igniting Counterflow (ICF) Flamelets. Findings of this study will broaden our knowledge on such a complex combustion regime, and provide reduced models for accurate RANS/LES simulations of turbulent Mild flames in the future.</p