The ferric chloride (FeCl3) murine model of thrombosis is used extensively in hematology, in which application of ferric chloride (200 mM to 1M) to the adventitial side of mouse arteries results in occlusive thrombosis. This effect has historically been attributed to the denudation of endothelial cells by way of free iron-induced oxidative stress. Recently, a well-designed SEM analysis revealed that endothelial cells actually remain intact, and that erythrocytes adhere to the endothelium prior to platelets (Barr, et al, Blood, 2013). The same study found that washed red blood cells exposed to FeCl3 adhere to endothelial cells in vitro. These novel findings inspired us to comprehensively investigate the mechanisms of FeCl3-induced thrombosis via an in vitro reductionist approach: interrogating the effect of FeCl3 on individual blood components in the absence and presence of endothelial cells.
This universal aggregation effect of FeCl3 led us to posit a charge-based hypothesis. Mechanistically, as Fe3+ ions bind negatively charged surfaces, such as cell membranes and plasma proteins, the intrinsic charge equilibrium of blood may shift, resulting in protein and cell aggregation. Indeed, erythrocyte suspensions exposed to Al3+, which is chemically similar to Fe3+, resulted in cell aggregation. In contrast, erythrocyte suspensions exposed to Cr3+, which forms substitutionally inert water complexes in solution and thus would not be expected to bind protein and cell surfaces, did not result in aggregation (Fig 2C). This suggests that inner-sphere complexation of Fe(III) to plasma proteins/endothelial or blood membranes may have a mechanistic role in FeCl3-induced thrombosis and further explains how the sheet-like protein aggregates could act as Fe3+ linkers that effectively enhances cell binding.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.