Methodological issues in biophysics

Reversible aggregation and deformation of RBC as determining factors of blood fluidity control

Background

Red blood cells (RBC) microrheologic properties (MP) strongly influence blood fluidity and, consequently, the microcirculation of blood and human health in general. These RBC intrinsic properties including their reversible aggregation and deformation in shear flow, in particular, in microcapillaries, change in various pathologies, e.g., due to elevated binding of fibrinogen, the major aggregation-inducing molecule in blood plasma, to RBC membrane. Changes in RBC MP can take place aiming to control blood fluidity endogenously by the organism itself or exogenously via medications.

Aims

This work aims to characterize the RBC aggregation, deformability, capillary flow and fibrinogen-membrane binding properties using in vitro and in vivo optical measurements.

Methods

We used RBC aggregometry method based on diffuse light scattering from whole blood samples in microfluidic flow chambers, laser diffractometry technique from dilute suspensions of RBC in controlled shear flow, laser trapping and manipulation of single RBC, and fluorescence microscopy and flow cytometry to assess the mechanisms of fibrinogen interaction with RBC membrane and possible ways to control it (all in vitro). These measurements were performed with blood samples freshly drawn from cubital veins of healthy volunteers or patients suffering from various diseases following their informed consent. The blood samples were always stabilized in order to prevent clotting. Also, we used digital capillaroscopy of blood flows in nail bed capillaries in vivo.

Results

The results of large series of measurements based on a group of healthy volunteers and several groups of patients suffering from arterial hypertension and type 2 diabetes mellitus show significant impairment of MP, in particular, enhancement of RBC aggregation both in large populations of cells and in cell doublets. Statistically significant correlation of these changes with alterations of blood capillary flow parameters was found, which indicates the control effect of the MP on blood fluidity. Our results on the effects of fibrinogen-binding inhibition, show the specific character of the adsorption of fibrinogen on RBC membrane. This indicates the existence of a fibrinogen receptor on the surface of RBC membrane, which may be a glycoprotein receptor class IIb/IIIa. This result potentially presents novel opportunities to control the rate of fibrinogen adsorption on RBC membrane and, therefore, correct the MP disorders caused by elevated fibrinogen-induced RBC aggregation.

Conclusions

Optical characterization of RBC microrheology and blood microcirculation performed using in vitro and in vivo measurements enables one to determine significant alterations in important features of human organisms that may need urgent clinically corrections.

Acknowledgment

The study was supported by RFBR (grant No19-52-51015).