Effect of propranolol as antiadhesive therapy in sickle cell disease

Abstract

Sickle red blood cells (SSRBCs) adhere to both endothelial cells (ECs) and the extracellular matrix. Epinephrine elevates cyclic adenosine monophosphate in SSRBCs and increases adhesion of SSRBCs to ECs in a β-adrenergic receptor and protein kinase A-dependent manner. Studies in vitro as well as in vivo have suggested that adrenergic stimuli like epinephrine may contribute to vaso-occlusion associated with physiologic stress. We conducted both animal studies and a Phase I dose-escalation study in sickle cell disease (SCD) patients to investigate whether systemically administered propranolol inhibits SSRBC adhesion and to document the safety of propranolol in SCD. Systemically administered propranolol prevented SSRBC adhesion and associated vaso-occlusion in a mouse model. In patients receiving a single oral dose of 10, 20, or 40 mg propranolol, SSRBC adhesion to ECs was studied before and after propranolol, with and without stimulation with epinephrine. Propranolol administration significantly reduced epinephrine-stimulated SSRBC adhesion in a dose dependent manner (p = 0.03), with maximum inhibition achieved at 40 mg. Adverse events were not severe, did not show dose dependence, and were likely unrelated to drug. No significant heart rate changes occurred. These results imply that β-blockers may have a role as antiadhesive therapy for SCD.

© 2012 Wiley Periodicals, Inc.

Figures

Figure 1

Epinephrine stimulates and propranolol blocks SSRBC adhesion to vessel walls in nude mice. Fluorescent‐labeled RBCs appeared gray when actively circulating but white when stationary due to adhesion to vessel walls. Mice were treated with IV saline or propranolol, followed by infusion of nonstimulated (sham‐treated) or epinephrine‐stimulated SSRBCs, as described in section Materials and Methods. After IV saline, sham‐treated human SSRBCs showed little adhesion to vessel walls (Panel A), while epinephrine‐stimulated SSRBCs showed marked adhesion to postcapillary venules, with intermittent vaso‐occlusion (Panel B). IV propranolol considerably reduced epinephrine‐stimulated SSRBC adhesion and occurrence of vaso‐occlusion (Panel C). Examples of SSRBC adhesion to vessel walls and vaso‐occlusion are shown by arrows in Panels B and C.

Figure 2

Effect of IV propranolol on the circulatory characteristics of human SSRBCs activated by epinephrine treatment. (A) Percentage of the vessel length occupied by SSRBCs. IV propranolol reduced the length of vessel walls occupied by epinephrine‐stimulated SSRBCs infused into nude mice. Vessels were observed through window chambers, as described in section Materials and Methods. (B) SSRBC flux measurements. IV propranolol treatment of mice improved the flux of epinephrine‐treated SSRBCs.

Figure 3

In vitro measures of SSRBC adhesion to endothelial cells. (A) Baseline adherence of SSRBCs to human umbilical vein endothelial cells (HUVECs) before and after stimulation of RBCs by epinephrine. SSRBCs were collected from study subjects at screening and again prior to treatment with oral propranolol. RBCs were shamtreated with buffer only or incubated with 20 nM epinephrine for 1 minute. Cells were then washed and tested for their ability to adhere to confluent cultures of HUVECs. Data represent mean and standard error of the mean (SEM) of composite values obtained for sheer stresses at 1, 2, and 3 dyne/cm2 for all patients. (B) Oral propranolol reduced SSRBC adhesion. Blood samples were obtained prior to propranolol treatment and 1 hour after a single dose of propranolol at the doses indicated. In each assay, SSRBCs were first exposed to epinephrine and then washed, as described. Oral propranolol treatment reduced adhesion of SSRBCs to HUVECs at 1–3 dyne/cm2 in a dose‐dependent manner. The gray area represents adhesion of nonepinephrine‐stimulated SS RBCs ± SEM. Error bars indicate SEM. p= 0.0004 for comparison of baseline unstimulated SSRBCs versus epinephrine‐stimulated SSRBCs (Panel A). p= 0.03 for comparison of baseline epinephrine‐stimulated SSRBCs versus epinephrine‐stimulated SSRBC adhesion to ECs after the 40 mg propranolol dose.

Figure 4

Effect of propranolol on blood pressure and heart rate in SCD. (A) The composite of the mean systolic and diastolic BP for all patients during the 6‐hour study period at the different study drug doses. (B) The composite of the mean heart rate (bpm = beats per minute) for all patients in each dose cohort during the 6‐hour study period.