Ameliorating effects of fluorocarbon emulsion on sickle red blood cell–induced obstruction in an ex vivo vasculature

Abstract

In sickle cell (SS) vaso-occlusion, the culminating event is blockage of blood vessels by sickled red blood cells (SS RBCs). As shown in animal models, SS RBC-induced vaso-occlusion is often partial, allowing for a residual flow, hence oxygen delivery to partially occluded vessels could reduce vaso-occlusion. The efficacy of an oxygenated perflubronbased fluorocarbon emulsion (PFE) was tested for its anti-vaso-occlusive effects in the ex vivo mesocecum vasculature of the rat. IntroductionSickle cell (SS) anemia is characterized by recurring episodes of painful vaso-occlusive crises and multiple organ damage. The pathophysiology of this disease is attributed to a single amino acid substitution at the sixth position of the ␤ chain (␤6, Glu3Val) of the hemoglobin (Hb)S molecule. This single-point mutation results in the polymerization of HbS and the sickling of red blood cells (RBCs) under deoxygenated conditions. At least 2 factors-in vivo sickling and RBC-endothelium interactions-would contribute to vaso-occlusion in sickle cell anemia. In sickling, vaso-occlusion results from the blockage of blood vessels by polymer-filled, nondeformable red cells. Adhesion of sickle red cells to vascular endothelium may narrow vessel lumen, increase red cell transit times, and allow cells with long delay times to polymerize and obstruct. 1 As observed in ex vivo 2 and in vivo models, 3 SS RBC-induced vaso-occlusion is often partial, allowing for decreased remnant flow. Hence, if oxygen is delivered to these areas, 4 decreased obstruction might be achieved. To this end, we have tested the efficacy of an oxygenated fluorocarbon emulsion for its anti-vasoocclusive effects.Fluorocarbon emulsion droplets (0.1-0.3 m) might deliver oxygen to sickled RBCs in partially obstructed vessels that cannot be reached by much larger oxygenated RBCs (approximately 8.0-m diameter). Fluorocarbons have high oxygen solubility through weak van der Waal forces. 5 There is a direct linear relation between oxygen tension and the amount of oxygen dissolved in fluorocarbons. 5,6 In addition, fluorocarbons are biologically inert because of the strong carbon-fluorine bonds. We hypothesize that partial vaso-occlusion by sickle RBCs could be reversed if we could deliver oxygen to the affected vessels. To this end, we have evaluated the efficacy of a fluorocarbon emulsion based on perflubron (C 8 F 17 Br) to ameliorate ensuing vaso-occlusion by SS red cells in an ex vivo preparation. Materials and methods Preparation of cellsHeparinized blood was obtained with informed consent from adult patients with sickle cell anemia (n ϭ 5) who were not in crisis and had not received blood transfusion in the preceding 4 months. After removal of the buffy coat, SS RBCs were suspended in autologous plasma, and the hematocrit (Hct) level was adjusted to 30%. SS RBC suspensions were deoxygenated in a rotatory tonometer (model IL 237; Instrumentation Laboratory, Lexington, MA). At the end of deoxygenation, samples were withdrawn anaerobically in syringes previously flushed wit...

Stimulation of erythrocyte ceramide formation by platelet-activating factor

“…Indeed, PAF has been shown to foster adherence of erythrocytes to endothelial cells (Sultana et al, 1999), to be involved in the formation of platelet-erythrocyte aggregates (Sirolli et al, 2001) and to mediate the systemic cardiovascular shock following antibody infusion (Tanaka et al, 2002). Moreover, it has been shown to participate in the vascular obstruction by dehydrated sickle cells (Kaul et al, 2000;Kaul et al, 2001). However, exposure of phosphatidylserine at the cell surface is thought to stimulate the uptake of erythrocytes by macrophages (Romero et al, 1999).…”

The contribution of endothelial cell P-selectin to the microvascular flow of mouse sickle erythrocytes in vivo

“…54 Although the adhesion of platelets and leukocytes to activated endothelial P-selectin [55][56][57] should have been blocked by the mAb combination that included anti-PSGL-1 mAb, it is possible that other P-selectin recognition determinants such as sulfatides 58 or glycoprotein Ib-IX-V 59 may have mediated the adhesion of nonerythroid cells to P-selectin on endothelial cells. Platelet activating factor (PAF) could have mediated the adhesion of sickle RBCs, [60][61][62] but the differences between the responses of P-selectin-deficient and wild-type mice suggest that a PAF effect was not a major one. We cannot exclude the possibility that TSP might have contributed to the changes we observed.…”

Studying Mechanisms of Eryptosis

“…Lang et al 2005c). Interestingly, these data can serve as an additional explanation for the PAF-mediated adherence of sickle erythrocytes to endothelium (Kaul et al 2000(Kaul et al , 2001.…”