Static magnetic fields induce blood flow decrease and platelet adherence in tumor microvessels.

Red blood cell flow in capillaries is reduced during exposure to strong static magnetic fields (SMFs). Intratumoral microcirculation is characterized by tortuous microvessels with chaotic architecture and by irregular, sluggish blood flow with unstable rheology. It was the aim of this study to analyze SMF exposure effects on tumor microcirculation with regard to interactions of corpuscular blood components with tumor microvessel walls. In vivo fluorescence microscopy was performed in A-Mel-3 tumors growing in dorsal skinfold chamber preparations of Syrian Golden hamsters. SMFs with varying field strength (< 600 mT) were generated by changing the distance between a strong NdFeB rod magnet and the tissue region of interest. Short-time exposure above a magnetic flux density of about 150 mT resulted in a significant reduction of red blood cell velocity (vRBC) and segmental blood flow in tumor microvessels. At the maximum strength of 587 mT, a reversible reduction of vRBC (approximately 40%) and of functional vessel densitiy (approximately 15%) was observed. Prolongation of the exposure time from 1 min to up to 3 h resulted in comparable reductions. Microvessel diameters and leukocyte-endothelial cell interactions remained unaffected by SMF exposure. However, in contrast to tumor-free striated muscle controls, exposure at the maximum flux density induced a significant increase in platelet-endothelial cell adherence in a time-dependent manner that was reversible after reducing SMF strength. These reversible changes may have implications for functional measurements of tumor microcirculation by MRI and new therapeutic strategies using strong SMFs.