to sustain tissue derangement and insulin resistance, linking diabetes to vascular disease. Given that diabetes is largely considered 
a pro-inflammatory condition, it is surprising that the role of anti-inflammatory cells has rarely been investigated. A current theory postulates that tissue injury in diabetes is worsened by impaired control of the inflammatory response, where the final steps are defective. Recent studies showed, that macrophages may display an “alternatively activated” phenotype, which enhances debris scavenging, angiogenesis and tissue remodeling. Among the markers that characterize this phenotype, the angiopoietin receptor has received particular attention because it favors the association of M2-like macrophages with blood vessels and regulates their ability to induce blood vessel formation in both physiologic and pathologic conditions. Importantly, the role of TEMs in the pathogenesis of vascular and tissue inflammation in diabetes has never been previously investigated. A number of emerging clinical and experimental reports suggest that continuous PDE5 inhibition is PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19786614 associated with cardioprotection, neuroprotection and wound healing. In type 2 diabetes patients, we have shown that chronic treatment with sildenafil, a PDE5 inhibitor, is associated with cardioprotection and reduced levels of circulating inflammatory cytokines. A promising role for PDE5i in the modulation of inflammatory processes has also been reported in ischemia-reperfusion injury in the heart and in renal damage. Although some of these studies reported improved circulating cytokine profiles and reduced oxidative stress after PDE5i administration, its effects on the composition of the macrophages involved in tissue infiltration remain unclear. The aim of this study is to investigate if PDE5i might mitigate the M1-type macrophage tissue infiltration induced by hyperglycemia by reducing vascular inflammation through specific modulation of TIE2 expressing monocytes. Materials and Methods Animal model Diabetes was induced in 12-week-old male CD1 mice using a single high-dose intraperitoneal injection of Streptozotocin dissolved in saline buffer. After 3 days Sildenafil was administered by i.p. daily, for 3 weeks or, in survival analysis, for 6 weeks. Appropriate vehicle controls were performed for each setting. Both housing and care of laboratory animals were in accordance with Italian law, and the study was approved by the Sapienza University’s Animal Research Ethics Committee. 2 / 17 PDE5 Inhibition Restores M2 Macrophages in Diabetic Mice Experimental design Mice were randomly assigned to 4 groups: CTRL and 7 mice for survival ), STZ, STZ + SILD and SILD. Short term observation was used for tissue macrophage infiltration/recruitment analysis and mid-term for the survival analysis. Mouse sample size was calculated assuming relevant a standardized mean difference of 2 in the percentage of resident TEMs with a 5% significance level and 90% power for independent twosided tests. All STZ-induced animals were supplied with 10% sucrose water for 72 h after STZ injection to counteract post-injection hypoglycemia. Housing of one mouse per cage allowed individual measurement of food and water intakes. A drop of tail blood after 3h fasting PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19786154 was used to monitor glucose concentrations by MediSense Precision Plus kit. Survival studies mice were inspected daily for signs of pain or distress, KU55933 custom synthesis including changes in respiration, appetite, urine output, excessive thirst,
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