Although red blood cell (RBC) life span is a known determinant of percentage hemoglobin A1c (HbA1c), its variation has been considered insufficient to affect clinical decisions in hematologically normal persons. However, an unexplained discordance between HbA1c and other measures of glycemic control can be observed that could be, in part, the result of differences in RBC life span. To explore the hypothesis that variation in RBC life span could alter measured HbA1c sufficiently to explain some of this discordance, we determined RBC life span using a biotin label in 6 people with diabetes and 6 nondiabetic controls.

Summary Modulation of intracellular chloride concentration ([Cl−]i) plays a fundamental role in cell volume regulation and neuronal response to GABA. Cl− exit via K-Cl cotransporters (KCCs) is a major determinant of [Cl−]I; however, mechanisms governing KCC activities are poorly understood. We identified two sites in KCC3 that are rapidly dephosphorylated in hypotonic conditions in cultured cells and human red blood cells in parallel with increased transport activity. Alanine substitutions at these sites result in constitutively active cotransport. These sites are highly phosphorylated in plasma membrane KCC3 in isotonic conditions, suggesting that dephosphorylation increases KCC3's intrinsic transport activity. Reduction of WNK1 expression via RNA interference reduces phosphorylation at these sites. Homologous sites are phosphorylated in all human KCCs. KCC2 is partially phosphorylated in neonatal mouse brain and dephosphorylated in parallel with KCC2 activation. These findings provide insight into regulation of [Cl−]i and have implications for control of cell volume and neuronal function.

• Sickle RBC ROS production is mediated in part by NADPH oxidase activity.• Sickle RBC ROS production can be induced by plasma signaling molecules.Chronic inflammation has emerged as an important pathogenic mechanism in sickle cell disease (SCD). One component of this inflammatory response is oxidant stress mediated by reactive oxygen species (ROS) generated by leukocytes, endothelial cells, plasma enzymes, and sickle red blood cells (RBC). Sickle RBC ROS generation has been attributed to sickle hemoglobin auto-oxidation and Fenton chemistry reactions catalyzed by denatured heme moieties bound to the RBC membrane. In this study, we demonstrate that a significant part of ROS production in sickle cells is mediated enzymatically by NADPH oxidase, which is regulated by protein kinase C, Rac GTPase, and intracellular Ca 21 signaling within the sickle RBC. Moreover, plasma from patients with SCD and isolated cytokines, such as transforming growth factor b1 and endothelin-1, enhance RBC NADPH oxidase activity and increase ROS generation. ROS-mediated damage to RBC membrane components is known to contribute to erythrocyte rigidity and fragility in SCD. Erythrocyte ROS generation, hemolysis, vaso-occlusion, and the inflammatory response to tissue damage may therefore act in a positive-feedback loop to drive the pathophysiology of sickle cell disease. These findings suggest a novel pathogenic mechanism in SCD and may offer new therapeutic targets to counteract inflammation and RBC rigidity and fragility in SCD. (Blood. 2013;121(11):2099-2107 IntroductionVaso-occlusion and hemolysis from the rigid and concurrently fragile red blood cells (RBC) in patients with sickle cell disease (SCD) cause a variety of acute and chronic manifestations ranging from frequent and severe painful crises to stroke and chronic organ failure. Chronic inflammation has emerged as an important pathogenic mechanism in SCD, and oxidative stress is increasingly recognized as a component of this chronic inflammatory state, inducing damage to a variety of subcellular and tissue structures. 1,2Patients with SCD have decreased plasma levels of glutathione, vitamin C, and vitamin E, presumably due to consumption by increased oxidant production. [3][4][5] RBC and other cell types show evidence of lipid peroxidation and oxidative damage to structural proteins.6-8 Additionally, plasma from SCD patients has elevated levels of advanced glycation end products 9,10 and products of lipid peroxidation (F-2 isoprostanes, malonaldehyde, and 4-hydroxynonenal), [11][12][13] all of which are markers of oxidative stress. There are several postulated mechanisms for the increased oxidative stress in patients with SCD. Sickle (SS) RBC reactive oxygen species (ROS) generation has been attributed to sickle hemoglobin auto-oxidation and iron-mediated Fenton chemistry reactions catalyzed by denatured heme moieties bound to the RBC membrane.14 Plasma hemoglobin and free heme resulting from chronic hemolysis generate superoxide radicals via the same nonenzymatic mechanisms. 15 In...