Activation of vascular endothelium plays an essential role in vasoocclusion in sickle cell disease. The anti-inflammatory agents dexamethasone and adhesion molecule-blocking antibodies were used to inhibit endothelial cell activation and hypoxia-induced vasoocclusion. Transgenic sickle mice, expressing human alpha-, beta(S)-, and beta(S-Antilles)-globins, had an activated vascular endothelium in their liver, lungs, and skin, as exhibited by increased activation of NF-kappaB compared with normal mice. NF-kappaB activation increased further in the liver and skin after sickle mice were exposed to hypoxia. Sickle mice had decreases in red blood cell (RBC) velocities and developed vasoocclusions in subcutaneous venules in response to hypoxia. Dexamethasone pretreatment prevented decreases in RBC velocities and inhibited vasoocclusions and leukocyte-endothelium interactions in venules after hypoxia. Dexamethasone treatment inhibited NF-kappaB, VCAM-1, and ICAM-1 expression in the liver, lungs, and skin of sickle mice after hypoxia-reoxygenation. VCAM-1 or ICAM-1 blockade with monoclonal antibodies mimicked dexamethasone by inhibiting vasoocclusion and leukocyte adhesion in sickle mice, demonstrating that endothelial cell activation and VCAM-1 and ICAM-1 expression are necessary for hypoxia-induced vasoocclusion in sickle mice. VCAM-1, ICAM-1, and vasoocclusion increased significantly 3 days after dexamethasone discontinuation, possibly explaining rebounds in vasoocclusive crises observed after withdrawal of glucocorticosteroids in sickle patients. We conclude that anti-inflammatory treatments that inhibit endothelial cell activation and adhesion molecule expression can inhibit vasoocclusion in sickle cell disease. Rebounds in vasoocclusive crises after dexamethasone withdrawal are caused by rebounds in endothelial cell activation.

Vascular inflammation, secondary to ischemia-reperfusion injury, may play an essential role in vaso-occlusion in sickle cell disease (SCD). To investigate this hypothesis, dorsal skin fold chambers (DSFCs) were implanted on normal and transgenic sickle mice expressing human a and b s /b s-Antilles globin chains. Microvessels in the DSFC were visualized by intravital microscopy at baseline in ambient air and after exposure to hypoxia-reoxygenation. The mean venule diameter decreased 9% (P < 0.01) in sickle mice after hypoxia-reoxygenation but remained constant in normal mice. The mean RBC velocity and wall shear rate decreased 55% (P < 0.001) in sickle but not normal mice after hypoxia-reoxygenation. None of the venules in normal mice became static at any time during hypoxia-reoxygenation; however, after 1 hr of hypoxia and 1 hr of reoxygenation, 11.9% of the venules in sickle mice became static (P < 0.001). After 1 hr of hypoxia and 4 hr of reoxygenation, most of the stasis had resolved; only 3.6% of the subcutaneous venules in sickle mice remained static (P = 0.01). All of the venules were flowing again after 24 hr of reoxygenation. Vascular stasis could not be induced in the subcutaneous venules of sickle mice by tumor necrosis factor alpha (TNF-a). Leukocyte rolling flux and firm adhesion, manifestations of vascular inflammation, were significantly higher at baseline in sickle mice compared to normal (P < 0.01) and increased 3-fold in sickle (P < 0.01), but not in normal mice, after hypoxia-reoxygenation. Plugs of adherent leukocytes were seen at bifurcations at the beginning of static venules. Misshapen RBCs were also seen in subcutaneous venules. Am.

Magnetic nanoparticles can be used for a variety of biomedical applications. They can be used in the targeted delivery of therapeutic agents in vivo, in the hyperthermic treatment of cancers, in magnetic resonance (MR) imaging as contrast agents and in the biomagnetic separations of biomolecules. In this study, a characterization of the movement and heating of three different types of magnetic nanoparticles in physiological systems in vitro is made in a known external magnetic field and alternating field respectively. Infra-red (IR) imaging and MR imaging were used to visualize these nanoparticles in vitro. A strong dependence on the size and the suspending medium is observed on the movement and heating of these nanoparticles. First, two of the particles (mean diameter d = 10 nm, uncoated Fe3O4 and d = 2.8 µm, polystyrene coated Fe3O4+γ-Fe2O3) did not move while only a dextran coated nanoparticle (d = 50 nm, γ-Fe2O3) moved in type 1 collagen used as an in vitro model system. It is also observed that the time taken by a collection of these nanoparticles to move even a smaller distance (5 mm) in collagen (∼100 min) is almost ten times higher when compared to the time taken to move twice the distance (10 mm) in glycerol (∼10 min) under the same external field. Second, the amount of temperature rise increases with the concentration of nanoparticles regardless of the microenvironments in the heating studies. However, the amount of heating in collagen (maximum change in temperature ΔTmax∼9 °C at 1.9 mg Fe ml−1 and 19 °C at 3.7 mg Fe ml−1) is significantly less than that in water (ΔTmax∼15 °C at 1.9 mg Fe ml−1 and 33 °C at 3.7 mg Fe ml−1) and glycerol (ΔTmax∼13.5 °C at 1.9 mg Fe ml−1 and 30 °C at 3.7 mg Fe ml−1). Further, IR imaging provides at least a ten times improvement in the range of imaging magnetic nanoparticles, whereby a concentration of (0–4 mg Fe ml−1) could bevisualized as compared to (0–0.4 mg Fe ml−1) by MR imaging. Based on these in vitro studies, important issues and parameters that require further understanding and characterization of these nanoparticles in vivo are discussed.

Magnetic nanoparticles can be used for a variety of biomedical applications. They can be used in the targeted delivery of therapeutic agents, as contrast agents in MR imaging and in the hyperthermic treatment of cancers. Previous studies using these particles have not dealt with a quantitative characterization of movement and heating of these particles in biological environments. In the present study, the thermal characteristics of magnetic nanoparticles in water and collagen were investigated. In other studies, the movement of these particles in collagen in a known magnetic field was studied; infra-red (IR) imaging was used to visualize these particles in vitro. The results show that the amount of temperature rise increases with the concentration of nanoparticles regardless of the microenvironments. However, the amount of heating in collagen is significantly less than water at the same nanoparticle concentration. IR imaging can be used to visualize these particles in vitro over a wide range of concentrations of these nanoparticles.