The regulation of blood vessel formation is of fundamental importance to many physiological processes, and angiogenesis is a major area for novel therapeutic approaches to diseases from ischemia to cancer. A poorly understood clinical manifestation of pathological angiogenesis is angiodysplasia, vascular malformations that cause severe gastrointestinal bleeding. Angiodysplasia can be associated with von Willebrand disease (VWD), the most common bleeding disorder in man. VWD is caused by a defect or deficiency in von Willebrand factor (VWF), a glycoprotein essential for normal hemostasis that is involved in inflammation. We hypothesized that VWF regulates angiogenesis. Inhibition of VWF expression by short interfering RNA (siRNA) in endothelial cells (ECs) caused increased in vitro angiogenesis and increased vascular endothelial growth factor (VEGF) receptor-2 (VEGFR-2)-dependent proliferation and migration, coupled to decreased integrin ␣v␤3 levels and increased angiopoietin (Ang)-2 release. ECs expanded from blood- IntroductionAngiogenesis, the formation of new vessels from pre-existing ones, occurs physiologically in specific circumstances such as wound healing and the menstrual cycle. Dysregulated angiogenesis contributes to the pathogenesis of many disorders, including diabetes, cancer, and macular degeneration (reviewed in Carmeliet 1 ). Angiogenic factors such as vascular endothelial growth factor (VEGF) and the angiopoietins (Ang) orchestrate signaling pathways that promote endothelial cell (EC) migration, proliferation, and ultimately the formation of a new vessel. VEGF-A is a major regulator of angiogenesis (reviewed in Grothey and Galanis 2 ) and acts on ECs mainly through VEGF receptor-2 (VEGFR-2), a tyrosine kinase receptor (reviewed in Olsson 3 ), to promote endothelial proliferation, migration, and sprouting of tip cells in the early stages of angiogenesis (reviewed in Gerhardt 4 ). Ang-1 and Ang-2, which bind to the endothelial Tie-2 receptor, act in the later stages of blood vessel formation and are essential for the maturation of a stable vascular network and for the maintenance of endothelial integrity (reviewed in Thomas and Augustin 5 ). Ang-1 and Ang-2 were originally identified as agonist and antagonist of Tie-2 signaling, respectively, with Ang-1 supporting EC survival and endothelial integrity 6 and Ang-2 promoting blood vessel destabilization and regression. 7 However, recent data suggest a more complex picture that includes cross-talk between the VEGF and the Ang pathways. 8 Growth factor signaling pathways are influenced by surface adhesion molecules that mediate cell-cell or cell-matrix interactions, particularly by members of the integrin superfamily. The integrin that has received most attention in ECs is ␣v␤3 (reviewed in Hodivala-Dilke 9 ), which mediates binding to several extracellular matrix proteins and growth factor receptors including VEGFR-2, thus influencing VEGFR-2 signaling (reviewed in Somanath et al 10 ). ␣v␤3 plays a complex role in angiogenesis. Although the origina...

Summary Thrombotic thrombocytopenic purpura (TTP) is a life‐threatening disorder and plasma exchange (PEX) remains the primary treatment modality. Twenty‐five patients with acute refractory/relapsing idiopathic TTP received rituximab in conjunction with PEX because of progressive clinical disease or deterioration in laboratory parameters, despite intensive standard therapy. In relapsing TTP, rituximab was started if antibody to ADAMTS‐13 (a disintegrin and metalloproteinase with thrombospondin motif‐13) was demonstrated during previous episodes. All 25 patients attained complete clinical and laboratory remission in a median of 11 d after initiating rituximab. In 21 cases, ADAMTS‐13 activity was within the normal range following rituximab. Inhibitors were detected in 24/25 patients by mixing studies and/or immunoglobulin G (IgG) antibodies to ADAMTS‐13 pre‐rituximab. There was no evidence of inhibitors and/or IgG activity <10% in 23/25 patients following rituximab. In acute refractory cases, the median number of PEX pre‐rituximab and following the first rituximab infusion was 13 and 9, respectively. There have been no infectious complications, despite low CD 19 levels and no relapses. In patients with acute refractory/relapsing idiopathic TTP, rituximab appears to be a safe, effective, targeted therapy with a significant reduction in the requirement for PEX.

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Pregnancy is an initiating event for acute thrombotic thrombocytopaenic purpura (TTP). There is a high risk of relapse during pregnancy and of foetal morbidity. We describe five cases with successful maternal and foetal outcomes in patients with a history of TTP. Cases 1 and 2 presented with TTP in their first pregnancy and had second-trimester foetal losses. Case 3 had four TTP relapses and soon after achievement of clinical remission became pregnant. Case 4 presented with TTP and left-sided stroke in pregnancy. ADAMTS-13 activity was less than 5% at presentation in four patients and prior to therapy during pregnancy in cases 1-4. Case 5, who had a single acute episode of TTP and became pregnant 6 years later, had normal ADAMTS-13 activity throughout pregnancy. Only case 3 had evidence of an inhibitor on mixing studies. All five patients underwent close haematological and obstetric monitoring and continued low-dose aspirin throughout pregnancy. Patients 1-4 had regular plasma exchange and received low molecular weight heparin during pregnancy. Patient 4 also received rituximab during the third trimester with no observed maternal or neonatal toxicity. Live healthy infants were delivered in all five cases in the third trimester. These findings suggest that successful pregnancy outcome is achievable in patients with a history of TTP and that patients with severely reduced ADAMTS-13 activity at the onset of pregnancy, necessitates regular plasma exchange during pregnancy.

Cardiovascular disease (CVD) is a major cause of death in smokers, particularly in those with chronic obstructive pulmonary disease (COPD). Circulating endothelial progenitor cells (EPC) are required for endothelial homeostasis, and their dysfunction contributes to CVD. To investigate EPC dysfunction in smokers, we isolated and expanded blood outgrowth endothelial cells (BOEC) from peripheral blood samples from healthy nonsmokers, healthy smokers, and COPD patients. BOEC from smokers and COPD patients showed increased DNA double-strand breaks and senescence compared to nonsmokers. Senescence negatively correlated with the expression and activity of sirtuin-1 (SIRT1), a protein deacetylase that protects against DNA damage and cellular senescence. Inhibition of DNA damage response by silencing of ataxia telangiectasia mutated (ATM) kinase resulted in upregulation of SIRT1 expression and decreased senescence. Treatment of BOEC from COPD patients with the SIRT1 activator resveratrol or an ATM inhibitor (KU-55933) also rescued the senescent phenotype. Using an in vivo mouse model of angiogenesis, we demonstrated that senescent BOEC from COPD patients are dysfunctional, displaying impaired angiogenic ability and increased apoptosis compared to cells from healthy nonsmokers. Therefore, this study identifies epigenetic regulation of DNA damage and senescence as pathogenetic mechanisms linked to endothelial progenitors' dysfunction in smokers and COPD patients. These defects may contribute to vascular disease and cardiovascular events in smokers and could therefore constitute therapeutic targets for intervention.