Association between Oxidative Stress, Genetic Factors, and Clinical Severity in Children with Sickle Cell Anemia.

OBJECTIVES: To investigate the associations between several sickle cell disease genetic modifiers (beta-globin haplotypes, alpha-thalassemia, and glucose-6-phosphate dehydrogenase deficiency) and the level of oxidative stress and to evaluate the association between oxidative stress and the rates of vaso-occlusive events. STUDY DESIGN: Steady-state oxidative and nitrosative stress markers, biological variables, genetic modulators, and vaso-occlusive crisis events requiring emergency admissions were measured during a 2-year period in 62 children with sickle cell anemia (58 SS and 4 Sß0). Twelve ethnic-matched children without sickle cell anemia also participated as healthy controls (AA) for oxidative and nitrosative stress level measurement. RESULTS: Oxidative and nitrosative stress were greater in patients with sickle cell anemia compared with control patients, but the rate of vaso-occlusive crisis events in sickle cell anemia was not associated with the level of oxidative stress. The presence of alpha-thalassemia, but not glucose-6-phosphate dehydrogenase deficiency or beta-globin haplotype, modulated the level of oxidative stress in children with sickle cell anemia. CONCLUSION: Mild hemolysis in children with alpha-thalassemia may limit oxidative stress and could explain the protective role of alpha-thalassemia in hemolysis-related sickle cell complications.

Differential effects of adenylyl cyclase-protein kinase A cascade on shear-induced changes of sickle cell deformability.

BACKGROUND: Erythrocyte deformability is impaired in sickle cell disease (SCD). The regulation of cytoskeletal protein organization plays a key role in erythrocyte deformability. The activation of adenylyl cyclase (AC)/cAMP/Protein kinase A (PKA) signaling pathway was associated with increased deformability in healthy erythrocytes, however the role of this pathway in SCD is unknown. OBJECTIVE: We evaluated mechanical responses of sickle red blood cells under physiological levels of shear stress and the possible link between their deformability and AC/cAMP/PKA signaling pathway. METHODS: The shearing of sickle red blood cells at physiological level (5 Pa) and the measurement of deformability were performed by a laser assisted optical rotational cell analyzer (LORRCA). RESULTS: Red blood cell deformability increased of 2.5-6.5% by blocking the activity of phosphodiesterase with Pentoxifylline (10µM) (p < 0.05). The inhibition of AC with SQ22536 (100µM) produced more significant rise in deformability (+4.8-12%, p < 0.01). No significant change was observed by the inhibition of PKA with H89 (10µM). CONCLUSION: Pentoxifylline and SQ22536 increased the deformability of sickle red blood cells under fluid shear stress. Modulation of the AC/cAMP/PKA pathway could have the potential to be an effective therapeutic approach for SCD through shear-induced improvements of RBC deformability.

Blood storage alters mechanical stress responses of erythrocytes.

BACKGROUND: Erythrocytes undergo irreversible morphological and biochemical changes during storage. Reduced levels of deformability have been reported for stored erythrocytes. Erythrocyte deformability is essential for healthy microcirculation. OBJECTIVE: The aim of this study is to evaluate shear stress (SS) induced improvements of erythrocyte deformability in stored blood. METHODS: Deformability changes were evaluated by applying physiological levels of SS (5 and 10 Pa) in metabolically depleted blood for 48 hours and stored blood for 35 days with citrate phosphate dextrose adenine-1 (CPDA-1). Laser diffractometry was used to measure erythrocyte deformability before and after application of SS. RESULTS: Erythrocyte deformability, as a response to continuous SS, was significantly improved in metabolically depleted blood, whereas it was significantly impaired in the blood stored for 35 days with CPDA-1 (p≤0.05). The SS-induced improvements of deformability were deteriorated due to storage and relatively impaired according to the storage time. However, deformability of stored blood after exposure to mechanical stress tends to increase at low levels of shear while decreasing at high SS levels. CONCLUSION: Impairment of erythrocyte deformability after storage may contribute to impairments in the recipient's microcirculation after blood transfusion. The period of the storage should be considered to prevent microcirculatory problems and insufficient oxygen delivery to the tissues.