WFU Physics Colloquium

TITLE: Effects of Red Blood Cells on Nitric Oxide Bioactivity

SPEAKER: Xiaohua Liu

TIME: Monday April 24, 2017 at 10:00 AM

PLACE: ZSR 204

Red blood cells (RBCs) as one of important cells in human blood vessel are abundant in hemoglobin (Hb). Hb has four heme ferrous sites for binding oxygen, nitric oxide (NO), carbon monoxide (CO) and other small molecules. NO as an endothelial derived relaxing factor is involved in many physiological and pathological processes. Its reaction with Hb is extremely fast. Because of RBCs’ unique biconcave shape and intrinsic membrane barrier, the rate of NO scavenging by encapsulated Hb in RBCs is limited and slower 1000 times than cell-free hemoglobin. During blood storage, the shape of RBCs tends to spherical conversion and membrane deformability reduced. Hemolysis from RBCs breaking down leads to low NO bioavailability. It is supposed that old stored RBCs scavenging more NO than young ones. We designed competition experiments and stop-flow spectroscopy to determine that older stored RBCs scavenging NO 1.7-1.8 times faster than fresh stored RBCs. Through computational simulation, to obtain this observed result, the RBC membrane permeability to NO has to increase 5 to 70 folds. Under hypoxic and acidic condition, nitrite is reduced to NO by deoxygenated hemoglobin. Since two states of Hb (R-state and T-state) are reversible under proper condition, Hb acts as an allosterically controlled nitrite reductase. Using electron paramagnetic resonance spectroscopy, chemiluminescent detection and platelet activation study, we confirmed that Hb plays primary role for nitrite reduction in human body. Meanwhile, nutrients also can modulate NO export. The nitrite bioactivation in RBCs senses to low oxygen and low nutrients areas. Due to the rate constant of Hb and NO reaction, NO formed in the RBC is not likely to escape scavenging. NO activity is preserved in as a nitrosothiol through a nitrosylation process. Our result found that the nitrite bioactivation is involved surface protein nitrosation. Nitric oxide synthase (NOS) is an enzyme for converting L-arginine to NO and citrulline. Arginase as another enzyme converts L-arginine to urea and L-ornithine. Nor-NOHA as arginase inhibitor is supposed to block the arginase pathway so that increase NO production. However, our data suggest that nor-NOHA reacts with hemoglobin to form nitrite and nitrate not through NO production.