Key endothelial cell angiogenic mechanisms are stimulated by the circulating milieu in sickle cell disease and attenuated by hydroxyurea.

As hypoxia-induced inflammatory angiogenesis may contribute to the manifestations of sickle cell disease, we compared the angiogenic molecular profiles of plasma from sickle cell disease individuals and correlated these with in vitro endothelial cell-mediated angiogenesis-stimulating activity and in vivo neovascularization. Bioplex demonstrated that plasma from patients with steady-state sickle cell anemia contained elevated concentrations of pro-angiogenic factors (angiopoietin-1, basic fibroblast growth factor, vascular endothelial growth factor, vascular endothelial growth factor-D and placental growth factor) and displayed potent pro-angiogenic activity, significantly increasing endothelial cell proliferation, migration and capillary-like structure formation. In vivo neovascularization of Matrigel plugs was significantly greater in sickle cell disease mice than in non-sickle cell disease mice, consistent with an up-regulation of angiogenesis in the disease. In plasma from patients with hemoglobin SC disease without proliferative retinopathy, anti-angiogenic endostatin and thrombospondin-2 were significantly elevated. In contrast, plasma from hemoglobin SC individuals with proliferative retinopathy had a pro-angiogenic profile and more significant effects on endothelial cell proliferation and capillary formation than plasma from patients without retinopathy. Hydroxyurea therapy was associated with significant reductions in plasma angiogenic factors and inhibition of endothelial cell-mediated angiogenic mechanisms and neovascularization. Thus, individuals with sickle cell anemia or hemoglobin SC disease with retinopathy present a highly angiogenic circulating milieu, capable of stimulating key endothelial cell-mediated angiogenic mechanisms. Combination anti-angiogenic therapy to prevent the progression of unregulated neovascularization and associated manifestations in sickle cell disease, such as pulmonary hypertension, may be indicated; furthermore, the benefits and drawbacks of the potent anti-angiogenic effects of hydroxyurea should be clarified.

Elevated plasma levels and platelet-associated expression of the pro-thrombotic and pro-inflammatory protein, TNFSF14 (LIGHT), in sickle cell disease.

Chronic vascular inflammation and endothelial activation may initiate vaso-occlusion in sickle cell disease (SCD). TNFSF14 (CD258; LIGHT), a recently-identified pro-thrombotic and pro-inflammatory tumour necrosis factor (TNF)-superfamily cytokine, has a potent activating effect on endothelial cells. We evaluated whether TNFSF14 production is altered in SCD and whether platelets contribute to this production. TNFSF14 was measured in platelet-free plasma from healthy-control individuals (CON), steady-state sickle cell anaemia (SCA), SCA on hydroxycarbamide therapy (SCAHC) and haemoglobin SC (HbSC) patients. Mean plasma TNFSF14 was significantly increased in SCA, SCAHC and HbSC, compared to CON individuals. In SCA/SCAHC patients, plasma TNFSF14, showed no correlation with haematological variables, but was significantly correlated with serum lactate dehydrogenase and inflammatory markers (CD40LG , IL8 and ICAM1). Platelet-membrane TNFSF14 expression was significantly augmented on SCA platelets, and correlated with platelet activation; furthermore, measurement of platelet TNFSF14 release indicated that platelets may be a major source of circulating TNFSF14 in SCA. Interestingly, high plasma TNFSF14 was significantly associated with elevated tricuspid regurgitant velocity (≥2·5 m/s) in a population of SCA/SCAHC patients. The pro-inflammatory and atherogenic cytokine, TNFSF14, could contribute to endothelial activation and inflammation in SCA; future investigations may confirm whether this protein contributes to major clinical complications of the disease, such as pulmonary hypertension, and represents a potential therapeutic target.