INTRODUCTION: The therapeutic application of ionizing radiation is associated with thrombotic events, but the exact underlying molecular mechanisms are still unclear. Tissue factor (TF), the primary initiator of blood coagulation, is essentially involved in the pathophysiology of thrombosis. Circulating monocytes have been identified to upregulate TF under inflammatory conditions and, thereby, enhance blood thrombogenicity. The study examines the effect of irradiation on the cellular procoagulability and TF protein expression of human peripheral blood mononuclear cells (PBMNCs) in a time period of 7 days. MATERIALS AND METHODS: Human PBMNCs were irradiated with 20 Gy. Procoagulability of PBMNCs, released microparticles and microparticle-free cell supernatant was analyzed by a chromogenic assay and TF protein expression quantified by TF ELISA. To determine whether irradiated PBMNCs and shed microparticles initiate plasma clotting, a one stage clotting assay was performed. RESULTS: We found a significant increase of PBMNC-associated procoagulant activity over a time period of 7 days post irradiation. Moreover, 3 days post irradiation PBMNCs initiated the plasma clotting faster than non-irradiated cells. An enhanced cellular TF protein concentration was persistently observed throughout the investigated time up to 7 days post irradiation. Microparticle-associated TF activity significantly increased 3 days post irradiation compared with the non-irradiated controls. PBMNC-derived microparticles post irradiation also initiated the plasma clotting faster than microparticles derived from controls. CONCLUSIONS: The results show irradiation to induce TF expression and to increase procoagulability of PBMNCs and cell-derived microparticles. This could be a possible mechanism by which ionizing radiation enhances blood thrombogenicity.
INTRODUCTION: The therapeutic application of ionizing radiation is associated with thrombotic events, but the exact underlying molecular mechanisms are still unclear. Tissue factor (TF), the primary initiator of blood coagulation, is essentially involved in the pathophysiology of thrombosis. Circulating monocytes have been identified to upregulate TF under inflammatory conditions and, thereby, enhance blood thrombogenicity. The study examines the effect of irradiation on the cellular procoagulability and TF protein expression of human peripheral blood mononuclear cells (PBMNCs) in a time period of 7 days. MATERIALS AND METHODS:Human PBMNCs were irradiated with 20 Gy. Procoagulability of PBMNCs, released microparticles and microparticle-free cell supernatant was analyzed by a chromogenic assay and TF protein expression quantified by TF ELISA. To determine whether irradiated PBMNCs and shed microparticles initiate plasma clotting, a one stage clotting assay was performed. RESULTS: We found a significant increase of PBMNC-associated procoagulant activity over a time period of 7 days post irradiation. Moreover, 3 days post irradiation PBMNCs initiated the plasma clotting faster than non-irradiated cells. An enhanced cellular TF protein concentration was persistently observed throughout the investigated time up to 7 days post irradiation. Microparticle-associated TF activity significantly increased 3 days post irradiation compared with the non-irradiated controls. PBMNC-derived microparticles post irradiation also initiated the plasma clotting faster than microparticles derived from controls. CONCLUSIONS: The results show irradiation to induce TF expression and to increase procoagulability of PBMNCs and cell-derived microparticles. This could be a possible mechanism by which ionizing radiation enhances blood thrombogenicity.