Erythrocyte MP heme induces endothelial damage and vasoocclusions. Mouse mesenteric resistances arteries were perfused with PSS alone, and initial diameters provided controls. Arterioles were then preconstricted with phenylephrine, and endothelium-dependent vasodilation was assessed in response to ACH (10−7 to 10−4 M). Arterioles were washed, constricted again with phenylephrine, and perfused with either SAD erythrocyte MPs (300 MPs/μL), or heme (100 nM) at 75 mm Hg pressure and 20 μL/s flow. (A) Endothelium-dependent vasodilation in response to increasing ACH doses (10−7 to 10−4 M) was quantified and expressed as percentage of passive diameter. *P < .05 vs SAD MPs (brown line) and heme (red dashes). (B) Some SAD MPs were pretreated with Hpx (1 µM, 1 hour) prior to perfusion. *P < .05 vs control; #P < .05 vs SAD MPs alone (+ none). To evaluate vasoocclusions in vivo, we injected 2 × 104 SAD erythrocyte MPs per mouse (brown) intravenously to SAD transgenic mice. We monitored kidney vasoocclusions by recording echo-Doppler velocity waveforms (C-D) and hemodynamic parameters. In each SAD mouse, we recorded the mean blood flow velocity (cm/s) in the right renal artery (blue line in Doppler velocity waveforms), before (none) or after intravenous injection of 2 × 104 SAD mouse erythrocyte MPs. Some MPs were preincubated with Hpx as previously described prior to injection. *P < .05 vs none. (E) Histologic analysis by Masson trichrome staining of SAD kidneys, 5 minutes after injection of SAD MPs, alone or preincubated with Hpx. Arrows show erythrocytes, with larger deposits and vascular congestion in SAD.
