Low-Level Mercury Can Enhance Procoagulant Activity of Erythrocytes: A New Contributing Factor for Mercury-Related Thrombotic Disease

BACKGROUND Associations between cardiovascular diseases and mercury have been frequently described, but underlying mechanisms are poorly understood. OBJECTIVES We investigate the procoagulant activation of erythrocytes, an important contributor to thrombosis, by low-level mercury to explore the roles of erythrocytes in mercury-related cardiovascular diseases. METHODS We used freshly isolated human erythrocytes and ex vivo and in vivo thrombosis models in rats to investigate mercury-induced procoagulant activity. RESULTS Prolonged exposure to low-dose mercuric ion (Hg(2+); 0.25-5 microM for 1-48 hr) induced erythrocyte shape changes from discocytes to echinocytes to spherocytes, accompanied by microvesicle (MV) generation. These MVs and remnant erythrocytes expressed phosphatidylserine (PS), an important mediator of procoagulant activation. Hg(2+) inhibited flippase, an enzyme that recovers PS into the inner leaflet of the cell membrane, and activated scramblase, an enzyme that alters lipid asymmetry in the cell membrane. Consistent with these activity changes, Hg(2+) increased intracellular calcium and depleted ATP and protein thiol. A thiol supplement reversed Hg(2+)-induced MV generation and PS exposure and inhibited the increase in calcium ion (Ca(2+)) and depletion of ATP, indicating that free-thiol depletion was critical to Hg(2+)-mediated procoagulant activity. The procoagulant activity of Hg(2+)-treated erythrocytes was demonstrated by increased thrombin generation and endothelial cell adhesion. We further confirmed Hg(2+)-mediated procoagulant activation of erythrocytes in ex vivo and in vivo rat thrombosis models, where Hg(2+) treatment (0.5-2.5 mg/kg) increased PS exposure and thrombus formation significantly. CONCLUSION This study demonstrated that mercury could provoke procoagulant activity in erythrocytes through protein-thiol depletion-mediated PS exposure and MV generation, ultimately leading to enhanced thrombosis.