Effect of Lead(IV) Acetate on Procoagulant Activity in Human Red Blood Cells

Lead (Pb) is a ubiquitously occurring environmental heavy metal which is widely used in industry and human life. Possibly due to a global industrial expansion, recent studies have revealed the prevalent human exposure to Pb and increased risk of Pb toxicity. Once ingested by human, 95% of absorbed Pb is accumulated into erythrocytes and erythrocytes are known to be a prime target for Pb toxicity. Most of the studies were however, focused on Pb2+ whereas the effects of Pb4+, another major form of Pb on erythrocytes are poorly understood yet. In this study, we investigated and compared the effects of Pb4+, Pb2+ and other heavy metals on procoagulant activation of erythrocytes, an important factor for the participation of erythrocytes in thrombotic events in an effort to address the cardiovascular toxicity of Pb4+. Freshly isolated erythrocytes from human were incubated with Pb4+, Pb2+, Cd2+ and Ag+ and the exposure of phosphatidylserine (PS), key marker for procoagulant activation was measured using flow cytometry. As a result, while Cd2+ and Ag+ did not affect PS exposure, Pb4+ and Pb2+ induced significantly PS exposure in a dose-dependent manner. Of a particular note, Pb4+ induced PS exposure with a similar potency with Pb2+. PS bearing microvesicle (MV), another important contributor to procoagulant activation was also generated by Pb4+. These PS exposure and MV generation by Pb4+ were well in line with the shape change of erythrocyte from normal discocytes to MV shedding echinocytes following Pb4+ treatment. Meanwhile, nonspecific hemolysis was not observed suggesting the specificity of Pb4+-induced PS exposure and MV generation. These results indicated that Pb4+ could induce procoagulant activation of erythrocytes through PS exposure and MV generation, suggesting that Pb4+ exposure might ultimately lead to increased thrombotic events.