Antioxidant Defense to Hemolysis Is Organ-Specific and Reflects a Heterogeneity in Vascular Permeability in Sickle Cell Disease.

Abstract 1537

Poster Board I-560

Sickle cell disease (SCD) is characterized by intravascular hemolysis generating cell-free hemoglobin at concentrations that exceed the scavenging capabilities of heme-binding plasma proteins. Heme is a major source of oxidative stress, which is widely known to increase vascular permeability and cause tissue edema. Barrier disruptive effects of oxidative stress can however be counterbalanced by adaptive antioxidant defenses. Hitherto, the identity of specific antioxidant enzymes and cognate mechanisms protecting individual organs from oxidative stress in SCD remains poorly defined. In this study, microarray analysis was performed using non-toxic concentrations of hemin to analyze mechanisms of antioxidant defense by the endothelium. Multiple candidate antioxidant enzymes were identified each differentially elevated in several major organs in anemic SCD mice compared to non-anemic heterozygote and hemizygote littermates. Remarkably, none of the antioxidants was elevated in the brain of sickle mice. Moreover, the antioxidant phenotype in the kidney, spleen and liver of sickle mice were predominantly acute while the sickle lung was characterized by a predominantly chronic antioxidant phenotype. This latter finding was confirmed in SCD patients with chronic lung disease. Antioxidant enzyme activity was significantly higher in the lungs of adult sickle mice aged 3-6 months than in younger mice aged 4-6 weeks (p=0.004). However, this enhanced antioxidant activity declined significantly in middle-age mice 11-13 months old (p=0.005). Vascular permeability assessed by extravsasation of Evans blue dye was normal in the brain of sickle mice of all ages in agreement with our data indicating absence of oxidative stress in this organ. On the contrary, vascular permeability in the lung, kidney and heart of adult sickle mice was abnormally high. This abnormality deteriorated significantly exclusively in the lung (p= 0.04) but not in the heart or kidney in middle-age mice. Increased lung permeability in middle-age sickle mice was confirmed by overt tissue edema determined by lung wet/dry weight ratios. Our study has shown for the first time that the antioxidant response to the systemic chronic hemolysis of SCD is organ-specific. Furthermore, we have identified decline of antioxidant reserve concomitant with tissue edema as potential age-dependant risk factors for fatal lung complications in SCD. Finally, our data provide a framework to develop targeted antioxidant therapies to preserve organ function in SCD.