Simulations of chemical and biological reactions of reactive oxygen species in cellular mechanism
Using computational modeling to solve biologically relevant differential equations.
The effect of microparticles (MPs) on Nitric Oxide (NO)-mediated vasodilation with and without intravascular flow on rat mesenteries in myograph
To determine whether MPs do enter the cell-free zone, we are studing the effect of MPs on NO-mediated vasodilation with and without intravascular flow by using isolated micro vessels in a myograph apparatus. The data so far show that, similar to the case of cell-free hemoglobin and dissimilar to the case of red blood cells, flow does not substantially influence vessel tone when MP-HbA is present.┬ Thus, MP-encapsulated hemoglobin (MP-HbA) probably does enter the cell-free zone. These data suggest that as little as 5 micromolar MP-HbA can reduce NO bioavailability upon transfusion of old blood, an amount that would be present after transfusion of just 1-2 units.
A cell free zone formed by Red blood cell flow in the rat mesentery vessel
Plasma NO-scavenging activity
We explored the relative role of cell-free hemoglobin and hemoglobin encapsulated in microparticles formed during blood storage in scavenging NO. We measured the NO consuming ability of NO in plasma of different age stored blood using a chemiluminescence-based assay. Our results show that both hemoglobin concentrations of free HbA and MPs increase along with blood aging. The proportion of hemoglobin concentration in MPs increases compared to cell-free hemoglobin as the blood ages.
Simulations of NO uptake by red blood cells (RBC) and by MPs derived from red cells
To explore the extent of NO scavenging by MP-encapsulated hemoglobin (MP-HbA) during blood transfusion, we modeled Nitric Oxide (NO) uptake by RBCs and MPs within a blood vessel using computer simulations on a COMSOL model. We found that membrane permeability appears to influence the rate of NO uptake by RBCs and MPs. In addition, the appearance of MPs in RBC cell free zone may significantly reduce NO bioavailability.
A image of the 2D model in static balance state
Stopped-flow absorption measurements of NO uptake by red blood cells under oxygenated and deoxygenated conditions with a viscous or non-viscous buffer
we conducted stopped-flow (SF) absorption measurements of NO uptake by red blood cells under oxygenated and deoxygenated conditions. To explore the role of external diffusion, we employed a viscous and non-viscous buffer. We found that the viscosity of the buffer had a substantial effect on external diffusion, supporting our computational simulations and previous reports that demonstrate the importance of external diffusion in limiting oxygen uptake by red blood cells.
Kinetics of Nitric Oxide reactivity with MP-HbA┬
We measured the binding kinetics of NO by MP-encapsulated hemoglobin under aerobic conditions and compared them to the rate of scavenging of NO by free Hb using a fast time-resolved flash photolysis technique. We found that MP-encapsulated hemoglobin scavenges NO 2.5 to 3 times slower than free Hb but still very fast compared to the 1000 times slower reaction of┬ NO with red blood cell encapsulated Hb.
Absorbance recorded after mixing MP-HbA and NO in a Pump-Probe experiment