Angiogenic effects of erythropoietin.

Erythropoietin (Epo) is a low-molecular weight glycoprotein hormone stimulator of erythropoiesis synthesized in the fetal liver and in the adult kidney. Moreover, Epo is a pleiotropic cytokine that exerts diverse biological effects in non-hematopoietic tissues, and angiogenesis is indicated as one of its extra-hematopoietic functions. The involvement of Epo in angiogenesis may be considered as subset of its role in improving overall tissue oxygenation and of its anti-apoptotic role. In this context, Epo may be considered as an endogenous stimulator of vessel growth during tumor progression, and inhibition of Epo signaling might be suggested as a new antiangiogenic therapeutic approach. It is conceivable suppose that the effect of Epo is multifactorial, depending on the type of tumor and level of functionality of Epo receptor expression in tumor cells, as well as on other variables, such as hypoxic stress and degree of anemia.