ALBERT

Description: Nuclear factor erythroid 2-related factor 2 (Nrf2) is the major transcription factor that coordinates the body's antioxidant and cytoprotective defense against a variety of toxins. Several Nrf2 activators can reactivate gamma globin gene expression and augment fetal hemoglobin production. More recently, genetic and pharmacologic evidence have shown that Nrf2 activation can specifically mitigate the severity of hemolytic anemia, and systemic and local inflammation in transgenic sickle cell disease (SCD) mice. Based on these encouraging results Nrf2 activation has emerged as an attractive therapeutic strategy in SCD. However, the BEACON trial of the Nrf2 activator CDDO-Methyl Ester (CDDO-Me) showed that this therapeutic approach can cause adverse cardiovascular events in patients with chronic kidney disease with comorbid diabetes. Hitherto, the efficacy-toxicity profile generated by individual Nrf2 activating drugs has not been investigated in SCD. There are hundreds of synthetic and naturally occurring Nrf2 activating compounds, and each class of Nrf2 activating compound has a unique pharmacokinetic, pharmacodynamic, toxicokinetic and toxicodynamic profile. We have recently demonstrated that intravascular hemolysis deteriorates with aging in transgenic sickle (SS) mice in a process that can be mitigated by the Nrf2 activator 3H-1,2-dithiole-3-thione (D3T) (Ghosh et al., JCI Insight, 2016). In this study, an in vitro screen of five Nrf2 activating compounds revealed CDDO-Me to be the most potent inducer of cytoprotective enzymes in human pulmonary microvascular endothelial cells. Thus, we performed a long-term prophylactic CDDO-Me treatment of SS mice and examined the effect of the drug on intravascular hemolysis and vascular dysfunction. A cohort of newly weaned SS mice aged ~4 weeks were randomly assigned to receive CDDO-Me (20µmoles/kg/TIW, n=6) or Vehicle (DMSO/TIW, n=10) by oral gavage for 4 months. After the treatment, the total hemoglobin increased by 10% in the CDDO-Me group while it decreased by 5% in the vehicle-treated group (p

Description: Acute chest syndrome (ACS) is a potentially fatal lung complication of sickle cell disease (SCD). There are currently no mechanistic based therapies for ACS and it continues to be a leading cause of death in SCD. Recent studies have identified independent links between extracellular heme with ACS, and with vaso-occlusive crisis (VOC) a common prodrome of ACS. Our experimental ACS model involves intravenous injection of purified hemin typically 35 µmoles/kg, which raises total plasma heme to a clinically relevant pathophysiologic level equivalent to ~0.5g/dl of hemoglobin, and causes respiratory failure exclusively in transgenic SCD mice of both the Townes and Berkeley strains (Ghosh et al., J Clin Invest, 2013). We have determined using time-lapse video microscopy and electrical cell impedance that hemin rapidly disrupts the pulmonary endothelial barrier in vitro. Hemopexin blocks hemin-induced pulmonary endothelial barrier disruption in vitro and respiratory failure in hemin-challenged SS mice. Importantly, genetic polymorphisms in the gene encoding heme oxygenase-1 the rate-limiting heme degradation enzyme are associated with ACS risk in the Cooperative Study of Sickle Cell Disease and the Silent Infarct Transfusion cohorts. These human data and our mechanistic results in SS mice support the heme hypothesis for ACS pathogenesis. P-selectin is a cell adhesion molecule involved in vascular inflammation. It is normally sequestered inside quiescent endothelium. However, recent evidence indicates extracellular heme activates the release of P-selectin unto the endothelial surface wall. Thus, in this study, we tested the hypothesis that P-selectin promotes ACS development. Infusion of a function blocking anti-P-selectin antibody protected SS mice (n=3) from hemin-induced ACS while all control SS mice (n=3) pretreated with IgG before the hemin challenge died (p=0.03) with severe hypoxemia and postmortem evidence of alveolar flooding. The apparent requirement for P-selectin in heme-induced lethal acute lung injury was confirmed by a 100% survival of P-selectin-/- (n=5) and 100% lethality of congenic P-selectin+/+ (n=5) mice challenged with hemin infusions (p=0.005). To identify the cell population involved in this disease process we generated bone marrow chimeric C57BL/6 mice lacking P-selectin in hematopoietic (P-selectinPLT-/-) and non-hematopoietic (P-selectinEC-/-) compartments. Seventy-five percent of P-selectinEC-/- mice were protected while all P-selectinPLT-/- congenic controls succumbed to hemin (n=3-4). The severity of lung injury in the P-selectinPLT-/- C57BL/6 mice was reflected by severe hypoxemia (SpO2: 82.75±2.14%) and a significantly higher lung wet/dry weight ratio compared to the ratio of the P-selectinEC-/- mouse lungs (p