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 Pb(2+) whereas the effects of Pb(4+), another major form of Pb on erythrocytes are poorly understood yet. In this study, we investigated and compared the effects of Pb(4+), Pb(2+) 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 Pb(4+). Freshly isolated erythrocytes from human were incubated with Pb(4+), Pb(2+), Cd(2+) and Ag(+) and the exposure of phosphatidylserine (PS), key marker for procoagulant activation was measured using flow cytometry. As a result, while Cd(2+) and Ag(+) did not affect PS exposure, Pb(4+) and Pb(2+) induced significantly PS exposure in a dose-dependent manner. Of a particular note, Pb(4+) induced PS exposure with a similar potency with Pb(2+). PS bearing microvesicle (MV), another important contributor to procoagulant activation was also generated by Pb(4+). These PS exposure and MV generation by Pb(4+) were well in line with the shape change of erythrocyte from normal discocytes to MV shedding echinocytes following Pb(4+) treatment. Meanwhile, nonspecific hemolysis was not observed suggesting the specificity of Pb(4+)-induced PS exposure and MV generation. These results indicated that Pb(4+) could induce procoagulant activation of erythrocytes through PS exposure and MV generation, suggesting that Pb(4+) exposure might ultimately lead to increased thrombotic events.