Co-Administration of Hydroxyurea and a Specific AKT2 Inhibitor Has Beneficial Effects on Acute Vaso-Occlusive Events and Survival in Sickle Cell Disease Mice

We recently demonstrated that the basal levels of AKT phosphorylation were significantly increased in neutrophils and platelets isolated from sickle cell disease (SCD) patients compared with those cells from healthy donors and that specific inhibition of AKT2 impaired neutrophil-endothelial cell and neutrophil-platelet interactions in venules of Berkeley (SCD) mice (Li et al. J Clin Invest 2014).  Although hydroxyurea (HU), an inducer of fetal hemoglobin, is the main therapy for treatment of SCD, it is unclear whether the short-term treatment with HU has immediate benefits on acute vaso-occlusive events in SCD. Using real-time fluorescence intravital microscopy, we demonstrated that co-administration of HU (100 microg/g body weight, iv injection) and Akti XII (3 microg/g body weight, iv injection), an AKT2 inhibitor, efficiently reduced neutrophil adhesion and platelet-neutrophil aggregation in cremaster muscle venules of TNF-α-challenged Berkeley mice. Importantly, compared with HU or Akti XII treatment alone, treatment with both agents significantly improved blood flow rates and survival in the mice. Further, similar results were obtained in Berkeley mice challenged with hypoxia (8% oxygen for 3 hours) and subsequent reoxygenation (room air for 3 hours). As determined by histochemistry of cremaster muscle sections following intravital microscopy of Berkeley mice, the expression of endothelial E-selectin and intercellular adhesion molecule 1 (ICAM-1) was significantly decreased by treatment with either HU or Akti XII. Leukocyte transmigration in the lung section of Berkeley mice was also inhibited by either agent, and the inhibitory effect was potentiated by co-administration of HU and Akti XII. Using the plasma and isolated cells of Berkeley mice, we found that the level of plasma nitric oxide species (NOx) was significantly elevated by treatment with HU but not Akti XII and that AKT2 phosphorylation levels in activated neutrophils and platelets were reduced by treatment with Akti XII but not HU. Taken together, these results suggest that short-term treatment of Berkeley mice with either HU or Akti XII inhibits inflammatory conditions: treatment with HU significantly increases plasma NOx levels, treatment with Akti XII decreases AKT2 phosphorylation in neutrophils and platelets without affecting plasma NOx levels, and administration of either agent reduces the surface expression of ICAM-1 and E-selectin on activated endothelial cells. Thus, our results provide evidence that co-administration of HU and a specific AKT2 inhibitor has immediate benefits on acute vaso-occlusive events and survival in SCD mice exceeding those seen for single therapy.