Fibrinogen and its Soluble Fibrin as Mediators of Erythrocyte Aggregation

Abstract

Erythrocyte (RBC) aggregation in blood or in plasma is a reversible phenomenon with an unknown mechanism. However there is evidence that it is induced, at least in part, by fibrinogen. RBC aggregation leads to vascular occlusion or flow diversion and shunting of oxygenated blood. If fibrinogen/fibrin ultimately becomes the major occlusive moiety, as one of us has observed in peri‐burn tissue at 48h post‐burn, the occlusion is likely to be irreversible. Previous studies exploring fibrinogen induced aggregation used Millipore fibrinogen. However, based on our preliminary observation of fibrinogen‐induced aggregation, we propose that the same concentration of fibrinogen across different company brands will induce aggregation of variable extent. Millipore fibrinogen was compared with isolated soluble fibrin‐depleted fibrinogen (FgD) and with soluble fibrin‐rich fibrinogen (FgR) (human). Using a spectrophotometer (Bio‐Rad SmartSpec 3000), focused on wavelengths of 540, 560, and 580nm, corresponding to a peak in oxy, deoxy, and oxygenated hemoglobin state in the RBCs, each fibrinogen isolated was tested at varying concentrations (1, 2, and 4mg/mL) and temperatures (32, 37, and 45°C) with washed human RBC. Across all temperatures and wavelengths, FgR fibrinogen dissolved in phosphate buffered saline (PBS) had a higher percent transmission, which correlates to an increased RBC aggregation, than both Millipore fibrinogen and FgD fibrinogen. Additionally, FgR induced the most aggregation at the highest tested concentration, 4mg/mL. Using this increased aggregation at 4mg/mL of FgR, we then compared to PBS and autologous platelet poor plasma. Across all temperatures, the magnitude of RBC aggregation is higher in plasma than FgR, which induces higher aggregation than PBS alone. The results demonstrated that fibrinogen‐induced RBC aggregation varies with the levels of its soluble fibrin/fibrinogen complex. By extension, these complexes clearly enhance RBC aggregation, intimating an in vivo role particularly in pathologic conditions that increase their levels.