VEGF AND ERYTHROPOIETIN, MESENCHYMAL STEM CELLS AND ENDOTHELIAL PROGENITOR CELLS: NEW ALTERNATIVES FOR ATROPHIC NON UNIONS

Abstract

Purpose: Athrophic non unions constitute a major problem in orthopaedic trauma. The main probably cause of atrophic non union is damage of the vascular system and dysfunctional regeneration of the vasculature at the area of the fracture. The most important hormonal pathway controlling angiogenesis is VEGF (Vascular Endothelial Growth Factor). The use of VEGF for enhancing bone healing in atrophic non unions could be a very promising solution for the future. An interesting alternative to the use of VEGF is the use of Erythropoietin (Epo). VEGF has been also reported to interact with Endothelial Progenitor Cells (EPCs). Our scope is to identify a possible new role for Epo as a valid substitute for VEGF through the clarification of the molecular and cellular pathways of fracture healing.

Methods: A survey was conducted via internet (Med-line - Pubmed, Cochrane database, Scopus) and relevant textbooks.

Results: It has been reported that Epo could induce increased chemotaxis, migration of Mesenchymal Stem Cells (MSCs), but also activation of Metaloproteinase - 9 and production of pro-angiogenic factors. These effects on MSCs could explain the observation that Epo could be very useful in the treatment of wound healing and burn healing in animal studies. It has been that Epo could express receptors at the chondrocytes, but also induce better bio-mechanical strength, callus formation, histomophometric image and increased bone density at the treated with Epo animals when compared with control animals. It is also worthy to note that the Epo has been found to stimulate neo-vascularisation in vivo, differentiation of endothelial cell lines towards a vascular pathway and improvement of cardiac function through EPCs and VEGF, implying Epo also in the differentiation and chemotaxis of the circulating EPCs. We should not forget that the transformation of EPCs in mesenchymal cells (i. g. myoblasts) has already been demonstrated.

Conclusions: The consequences of these observations could be very interesting: EPCs have been reported to enhance neo-vascularisation and angiogenesis at the region of the fracture. All these imply a novel role for EPCs in combination (or even replacing the rare) MSCs under the influence of VEGF and Epo for the enhancement of fracture vascularisation and healing enhancement. Further studies should clarify this new field in basic orthopaedic, trauma and bone metabolism science.