In vivo blood flow abnormalities in the transgenic knockout sickle cell mouse

Abstract

The accepted importance of circulatory impairment to sickle cell anemia remains to be verified by in vivo experimentation. Intravital microscopy studies of blood flow in patients are limited to circulations that can be viewed noninvasively and are restricted from deliberate perturbations of the circulation. Further knowledge of sickle blood flow abnormalities has awaited an animal model of human sickle cell disease. We compared blood flow in the mucosal-intestinal microvessels of normal mice with that in transgenic knockout sickle cell mice that have erythrocytes containing only human hemoglobin S and that exhibit a degree of hemolytic anemia and pathological complications similar to the human disease. In sickle cell mice, in addition to seeing blood flow abnormalities such as sludging in all microvessels, we detected decreased blood flow velocity in venules of all diameters. Flow responses to hyperoxia in both normal and sickle cell mice were dramatic, but opposite: Hyperoxia promptly slowed or halted flow in normal mice but markedly enhanced flow in sickle cell mice. Intravital microscopic studies of this murine model provide important insights into sickle cell blood flow abnormalities and suggest that this model can be used to evaluate the causes of abnormal flow and new approaches to therapy of sickle cell disease.

Figure 1

Frame-captured images from videotaped intravital microscopy of the mesenteric microcirculations of control and SCD mice. (a) Image of the microcirculation in a control mouse. Regular flow is indicated by uniformity of flow presentation in large (top right) and small (bottom) vessels, which is noticeably different from that in b. (b) Image of the microcirculation in an SCD mouse. Occluded blood flow is indicated by the abrupt transition between the dark, sludged (SS RBC–rich) blood below the open arrow and the lighter blood above it. Clumps of SS RBC apparently adherent to the wall of the same vessel also are visible (filled arrows). SCD, sickle cell disease; SS RBC, sickle red blood cell.

Figure 2

Blood flow velocities in control and SCD mice. The bar graph demonstrates paired mean V_rbc in small, medium, and large venules of control and SCD mice. The error bars indicate SD; the ordinate is blood flow velocity, V_rbc (mm/s); for each bar, n = 10.

Figure 3

Frame-captured images from videotaped intravital microscopy of the mesenteric microcirculations of SCD mice during normoxic and hyperoxic conditions. (a) Sludged flow of normoxic SCD blood indicated by discontinuous columns of RBC. A site of vaso-occlusion (filled arrow) has apparently distended the vessel proximally (top open arrow) and vacated the vessel of blood distally (bottom open arrow). (b) Improved flow of hyperoxic SCD blood indicated by less distention of the proximal vessel (top open arrow) and return of blood flow distally (bottom open arrow). RBC, red blood cell.

Figure 4

Changes in venular blood flow parameters of SCD and control mice induced by hyperoxia. Data pairs representing flow parameter values are shown as open circles connected by lines, the slope of which reflects the change in the parameter induced by hyperoxia. The top panels contain data from control mice, and the bottom panels contain data from SCD mice. (a and b) V_rbc data; (c and d) V_mean data; (e and f) wall shear rate; (g and h) volume metric flow rate (Q). The units for each parameter are shown in the ordinate labels. For both the control and SCD mice, n = 5.