Dipyridamole increases human red blood cell deformability

Substrate binding and inhibition of the anion exchanger 1 transporter

Anion exchanger 1 (AE1), a member of the solute carrier (SLC) family, is the primary bicarbonate transporter in erythrocytes, regulating pH levels and CO2 transport between lungs and tissues. Previous studies characterized its role in erythrocyte structure and provided insight into transport regulation. However, key questions remain regarding substrate binding and transport, mechanisms of drug inhibition and modulation by membrane components. Here we present seven cryo-EM structures in apo, bicarbonate-bound and inhibitor-bound states. These, combined with uptake and computational studies, reveal important molecular features of substrate recognition and transport, and illuminate sterol binding sites, to elucidate distinct inhibitory mechanisms of research chemicals and prescription drugs. We further probe the substrate binding site via structure-based ligand screening, identifying an AE1 inhibitor. Together, our findings provide insight into mechanisms of solute carrier transport and inhibition.

Red blood cell vesiculation in hereditary hemolytic anemia

Hereditary hemolytic anemia encompasses a heterogeneous group of anemias characterized by decreased red blood cell survival because of inherited membrane, enzyme, or hemoglobin disorders. Affected red blood cells are more fragile, less deformable, and more susceptible to shear stress and oxidative damage, and show increased vesiculation. Red blood cells, as essentially all cells, constitutively release phospholipid extracellular vesicles in vivo and in vitro in a process known as vesiculation. These extracellular vesicles comprise a heterogeneous group of vesicles of different sizes and intracellular origins. They are described in literature as exosomes if they originate from multi-vesicular bodies, or as microvesicles when formed by a one-step budding process directly from the plasma membrane. Extracellular vesicles contain a multitude of bioactive molecules that are implicated in intercellular communication and in different biological and pathophysiological processes. Mature red blood cells release in principle only microvesicles. In hereditary hemolytic anemias, the underlying molecular defect affects and determines red blood cell vesiculation, resulting in shedding microvesicles of different compositions and concentrations. Despite extensive research into red blood cell biochemistry and physiology, little is known about red cell deformability and vesiculation in hereditary hemolytic anemias, and the associated pathophysiological role is incompletely assessed. In this review, we discuss recent progress in understanding extracellular vesicles biology, with focus on red blood cell vesiculation. Also, we review recent scientific findings on the molecular defects of hereditary hemolytic anemias, and their correlation with red blood cell deformability and vesiculation. Integrating bio-analytical findings on abnormalities of red blood cells and their microvesicles will be critical for a better understanding of the pathophysiology of hereditary hemolytic anemias.

Reduced red blood cell deformability in patients with rheumatoid vasculitis. Improvement after in vitro treatment with dipyridamole

OBJECTIVE

To assess red blood cell deformability (RCD) in patients with rheumatoid arthritis (RA) without extraarticular manifestations and in RA with vasculitic complications (RV), and to assess whether in vitro dipyridamole improves RCD.

METHODS

An improved filtration technique was used to measure RCD in 15 patients with RA, 18 patients with RV, and 20 age- and sex-matched normal control subjects. Washed erythrocytes suspended in buffer, at 5% hematocrit, were filtered through 4.7 mu Nuclepore Hemafil PC membranes. The initial steady-state relative filtration pressure (iRFP) was used as an index to assess RCD. A lower iRFP value reflects increased deformability, a higher value reflects a decrease. For each sample, 2 cell suspensions were prepared, one blank (control) and one containing 5 microM dipyridamole.

RESULTS

The mean iRFP values of cells obtained from patients with RV were significantly higher than those of cells obtained from normal controls. There were no appreciable differences in iRFP between RA patients and normal controls. When the erythrocytes were pretreated in vitro with 5 microM dipyridamole before filtration, their deformability improved markedly (iRFP values were reduced) in all study subjects, compared with untreated cells.

CONCLUSION

RCD is reduced in patients with RV, and treatment with dipyridamole may be beneficial if reduced RCD contributes to impaired microvascular perfusion.