• Neurovascular Injury After Retinal Ischemia Reperfusion Insult: Contrasting Roles Of Arginase Enzyme Isoforms

      Shosha, Esraa; Vascular Biology Center (2016-03-08)
      Purpose: We have previously shown the involvement of arginase enzyme in retinal neurovascular injury. The present study was undertaken to determine the distinct roles of arginase 1 (A1) and arginase 2 (A2) in neurovascular damage following ischemia/reperfusion (I/R) injury. Methods: We used wild type (WT) mice, A2 knock out mice (A2-/-) and mice lacking one copy of A1 (A1+/-). Western blotting, RT-PCR, vascular digests, immunofluorescence, Propidium Iodide (PI) labeling and electroretinography (ERG) were used to evaluate retinal injury and function. Results: I/R injury caused significant increases in A2 expression along with thinning of the neural retina, decreases in NeuN+ GCL neurons and formation of acellular capillaries. Increases in PI labeling and RIP-3 expression showed that cell death occurred by necroptosis. Neurovascular injury was accompanied by microglial activation along with increased expression of GFAP and impairment of the ERG. Neuronal cell loss, capillary degeneration, necroptosis, gliosis and ERG impairment were all significantly reduced by deletion of A2. On the other hand, A1 deletion exacerbated I/R-induced neuronal and vascular injury and further increased necroptosis and gliosis as compared with WT retinas. Conclusions: This study shows for the first time the different roles of arginase isoforms after I/R insult. I/R-induced necrotic cell death and gliosis are mediated by A2, whereas upregulation of A1 may play a role in limiting the pathology.
    • Sustained Release Formulation for Vascular Endothelial Growth Factor

      Elzinga, Jennifer Lynn; Department of Oral Biology (2013-03)
      Necrosis of tissue due to trauma or a surgical procedure is a complication of wound healing. This necrosis, or tissue death, occurs when the vasculature is unable to perfuse involved tissue with the oxygen and nutrients necessary to maintain viability. To provide adequate access, reflecting a flap of tissue is often necessary in a variety of surgical procedures, including periodontal surgeries. The success of these procedures is limited by the development of tissue flap necrosis. The survival of these tissue flaps is dependent upon adequate perfusion by the blood vessel supply at the base of the flap, followed by the growth of new vascular channels from the recipient site. However, if angiogenesis does not promptly reach the distal extent of the flap, this portion becomes ischemic, leading to necrosis. Loss of the protective flap delays healing and increases the risk of scarring and infection. Necrosis of this distal region of a tissue flap begins as early as 24 hours following the surgical procedure and progresses rapidly until day 3 when the unaffected tissue begins to stabilize.1 A variety of pharmacological strategies to enhance tissue flap perfusion have been tested in an attempt to prevent necrosis. One such strategy is the administration of angiogenic growth factors such as vascular endothelial growth factor (VEGF). VEGF is known to stimulate the proliferation of endothelial cells from existing vasculature to create new blood vessels, thus enhancing 8 tissue survival.2-7 In addition, VEGF contributes to other aspects of wound healing, including inflammation, granulation tissue formation, reepithelialization, matrix formation, and remodeling.2 Administration of VEGF to wound healing models has shown promising results by increasing vascular formation, leading to enhanced tissue perfusion. However, its short duration of action and rapid dissipation from the target site reduces its effectiveness.8 Maintaining therapeutic concentrations of VEGF at the target site to maximize new vessel growth and reduce necrosis, either multiple applications or an extended-release delivery system is required. An ideal system would provide ease of use and delivery kinetics for sustained therapeutic dosing of VEGF to the wound environment for the duration of healing, thereby minimizing tissue necrosis. A variety of application methods and delivery systems are under investigation in the search to develop one that provides utility as well as improved clinical outcome.