Antisickling effect of bepridil

Bepridil as an antisickling agent: membrane internalization and cell rigidity

The calcium channel antagonist, bepridil, beta-(2-methylpropoxy)methyl-N-phenyl-N-(phenylmethyl)-1-pyrrol idineethanamine monochloride monohydrate, inhibits the sickling of deoxygenated sickle (SS) erythrocytes, as determined by light microscopy. The anti-sickling effect was seen only in dilute suspensions of red cells. In concentrated erythrocyte suspensions, sickling was not inhibited and measurements of hematocrit and cell density were unchanged by bepridil. The determination of cell volume in dilute suspensions was complicated by bepridil's tendency to aggregate, but rapid measurements by electronic sizing also indicated no increase in cell volume, up to a bepridil concentration of 200 microM. Ektacytometry of dilute sickle cell suspensions suggested an explanation for the anti-sickling action of bepridil. Osmotic scan ektacytometry disclosed that bepridil initially increased the surface area of the red cell, as shown by a shift in the low osmolality minimum. This change was complete in 10 sec, the shortest time that could be measured. Subsequently, at concentrations that were observed to inhibit the sickling of deoxygenated sickle cells (100 microM or greater), red cells underwent a loss in surface area that was complete in 1 min. There was a concomitant loss of cell deformability. Light and scanning electron microscopy has previously shown that bepridil is a stomatocytic agent. Using transmission electron microscopy, we verified that the loss of surface area was a consequence of endocytosis, presumably as the end stage of the stomatocytic transformation induced by bepridil. Bepridil did not inhibit intracellular hemoglobin S polymerization even at 200 microM, as shown by oxygen scan ektacytometry. Bepridil thus appears to inhibit the sickling of deoxygenated SS cells by inducing endocytosis and lowering cell deformability. This mechanism may explain the anti-sickling effect of other basic amphiphiles, such as chlorpromazine.

Dose-dependent red blood cell volume increase induced by bepridil

1. Bepiridil, (beta-[(2-methylpropoxy)methyl]-N-phenyl-N-(phenyl-methyl)-1-py rro lidine-ethanamine), a calcium channel blocker, inhibits sickling of red blood cells (RBC) from patients with sickle cell disease (SCD) at micromolar concentrations in vitro. 2. Bepridil induces dose-dependent osmotic swelling of RBC and a concomitant decrease in mean corpuscular hemoglobin concentration (MCHC). 3. Modest decreases in MCHC greatly lengthen the delay time for polymerization of deoxygenated sickle hemoglobin (Hb S) and inhibit RBC sickling. 4. Equilibrium dialysis studies of bepridil and purified hemoglobin showed a low binding affinity (Kb = 10(3)/M). 5. The partition coefficient (Kp) determined for the interaction of RBC and bepridil was 1-3 x 10(3), which is similar to the Kp determined for other amphipathic molecules, such as chlorpromazine.