MEK inhibitors, novel anti-adhesive molecules, reduce sickle red blood cell adhesion in vitro and in vivo, and vasoocclusion in vivo.

Rahima Zennadi

doi:10.1371/journal.pone.0110306

Abstract

In sickle cell disease, sickle erythrocyte (SSRBC) interacts with endothelial cells, leukocytes, and platelets, and activates coagulation and inflammation, promoting vessel obstruction, which leads to serious life-threatening complications, including acute painful crises and irreversible damage to multiple organs. The mitogen-activated protein kinase, ERK1/2, is abnormally activated in SSRBCs. However, the therapeutic potential of SSRBC ERK1/2 inactivation has never been investigated. I tested four different inhibitors of MEK1/2 (MEK), the kinase that activates ERK1/2, in a model of human SSRBC adhesion to TNFα-activated endothelial cells (ECs). SSRBC MEK inhibition abrogated adhesion to non-activated and TNFα-activated ECs to levels below baseline SSRBC adhesion to non-activated ECs in vitro. SSRBC MEK inhibition also prevented SSRBCs from activating naïve neutrophils to adhere to endothelium. To determine the effect of MEK inhibitors on SSRBC adherence in vivo, sham-treated or MEK inhibitor-treated SSRBCs were infused to nude mice previously treated with TNFα. Sham-treated SSRBCs displayed marked adhesion and occlusion of enflamed vessels, both small and large. However, SSRBC treatment with MEK inhibitors ex vivo showed poor SSRBC adhesion to enflamed vessels with no visible vasoocclusion in vivo. In addition, MEK inhibitor treatment of SSRBCs reduced SSRBC organ trapping and increased the number of SSRBCs circulating in bloodstream. Thus, these data suggest that SSRBC ERK1/2 plays potentially a critical role in sickle pathogenesis, and that MEK inhibitors may represent a valuable intervention for acute sickle cell crises.

Highlights

In sickle cell disease (SCD), sickle red blood cells (SSRBCs) have been postulated to play a central role in vasoocclusion by adhering to the endothelium, leukocytes and platelets in capillaries and small vessels, and activating coagulation and inflammation
We have discovered that MEK and ERK1/2 are highly expressed in both SSRBCs and normal RBCs, ERK1/2 is abnormally activated only in SSRBCs, but not in normal RBCs [18]
My present data reveal a potential contribution of SSRBC MEKdependent ERK1/2 activation in the vasoocclusive process, by which human SSRBCs both adhere to the vascular endothelium and act as a stimulus activating adhesion of human polymorphonuclear neutrophils (PMNs) to normal endothelial cells

Summary

Introduction

In sickle cell disease (SCD), sickle red blood cells (SSRBCs) have been postulated to play a central role in vasoocclusion by adhering to the endothelium, leukocytes and platelets in capillaries and small vessels, and activating coagulation and inflammation. Investigators have targeted SSRBCs and explored multiple approaches to treating acute vasoocclusive crises. Therapies that focus on ameliorating SSRBC dehydration [7,8,9,10,11], interfering with chemical-physical processes during erythrocyte-endothelial adhesion events [12], or targeting RBC adhesion molecules [13,14,15] to prevent RBC-endothelial cell (EC) interactions have shown little to no therapeutic benefit. An in-depth understanding of signaling pathways in SSRBCs that mediate adhesion at both biochemical and physiological levels will be required to successfully exploit these pathways for therapeutic purposes and to develop efficacious pathway-selective drugs with minimal side effects

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Conclusion