Xanthine Oxidase Drives Hemolysis and Vascular Malfunction in Sickle Cell Disease

Abstract

Objective: Chronic hemolysis is a hallmark of sickle cell disease (SCD) and a driver of vasculopathy; however, the mechanisms contributing to hemolysis remain incompletely understood. Although XO (xanthine oxidase) activity has been shown to be elevated in SCD, its role remains unknown. XO binds endothelium and generates oxidants as a byproduct of hypoxanthine and xanthine catabolism. We hypothesized that XO inhibition decreases oxidant production leading to less hemolysis. Approach and Results: Wild-type mice were bone marrow transplanted with control (AA) or sickle (SS) Townes bone marrow. After 12 weeks, mice were treated with 10 mg/kg per day of febuxostat (Uloric), Food and Drug Administration–approved XO inhibitor, for 10 weeks. Hematologic analysis demonstrated increased hematocrit, cellular hemoglobin, and red blood cells, with no change in reticulocyte percentage. Significant decreases in cell-free hemoglobin and increases in haptoglobin suggest XO inhibition decreased hemolysis. Myographic studies demonstrated improved pulmonary vascular dilation and blunted constriction, indicating improved pulmonary vasoreactivity, whereas pulmonary pressure and cardiac function were unaffected. The role of hepatic XO in SCD was evaluated by bone marrow transplanting hepatocyte-specific XO knockout mice with SS Townes bone marrow. However, hepatocyte-specific XO knockout, which results in >50% diminution in circulating XO, did not affect hemolysis levels or vascular function, suggesting hepatocyte-derived elevation of circulating XO is not the driver of hemolysis in SCD. Conclusions: Ten weeks of febuxostat treatment significantly decreased hemolysis and improved pulmonary vasoreactivity in a mouse model of SCD. Although hepatic XO accounts for >50% of circulating XO, it is not the source of XO driving hemolysis in SCD.

Cooperation between CYB5R3 and NOX4 via coenzyme Q mitigates endothelial inflammation

“…Cellular production of H 2 O 2 was evaluated by its fluorescent reaction product with coumarin boronic acid (Cayman, 14051) in the presence of l -NAME (Cayman, 80210) and taurine (Cayman, 27031) [ [31] , [32] , [33] ]. Coumarin boronic acid (CBA) is a sensitive probe for hydrogen peroxide, but necessary control must be included to rule out interference from peroxynitrite and hypochlorous acid.…”

Endothelial superoxide dismutase 2 is decreased in sickle cell disease and regulates fibronectin processing

“…Transfected hPMVECs were tryspinized and then resuspended in Mg 2 and Ca 2+ free Hank's Balanced Salt Solution (HBSS). In a 96 well plate 150 000 cells and 5 μM MitoSOX Red™ (Invitrogen) were added.…”

“…Sickle cell disease (SCD) is an inherited hemoglobinopathy that results in sickling of deoxygenated red blood cells (RBC) due to a point mutation in the beta-globin gene. 1 In SCD, there is an increase in oxidative stress due to augmented reactive oxygen species (ROS) production from enzymatic sources such as xanthine oxidase 2 and non-enzymatic sources including Fenton chemistry. 3 Paired with this increase in ROS production is a compromised antioxidant system.…”

Hyperuricemia and abnormal nocturnal dipping impact glomerular filtration rate in patients with sickle cell anemia

“…A study of febuxostat also did not demonstrate an overall benefit to patients with stage three kidney disease, but did show a benefit in patients without proteinuria or better initial kidney function at baseline. 6 Murine SCA models have demonstrated that hyperuricemia is associated with hemolysis and treatment with febuxostat improved the hemolytic phenotype.. 7 This association between uric acid and change and eGFR in SCA will need to be confirmed in a prospective randomized controlled trial of uric acid lowering medication.…”

“…We utilized the clinical documentation and radiological reports/images to assess the ORR based on the criteria described previously in prospective and retrospective adult histiocytosis studies. [7][8][9][10][11] We captured the best response, either clinical or radiological, depending on the organ involvement. Among patients with isolated skin involvement, response assessment was based on clinical examination.…”