Exposuretoa MRI-Type High-Strength Static Magnetic Field Stimulates Megakaryocytic/ Erythroid Hematopoiesis in CD34 + Cells From Human Placentaland Umbilical Cord Blood Satoru Monzen, 1 Kenji Takahashi, 1 TsutomuToki, 2 Etsuro Ito, 2 Tomonori Sakurai, 1 Junji Miyakoshi, 1 and Ikuo Kashiwakura 1 * 1 Department of RadiologicalLife Sciences, Division of MedicalLife Sciences, Hirosaki University Graduate Schoolof Health Sciences, Hirosaki, Japan 2 Department of Pediatrics, HirosakiUniversity Graduate Schoolof Medicine, Hirosaki, Japan The biological response after exposure to a high-strength static magnetic field (SMF) has recently been widely discussed from the perspective of possible health benefits as well as potential adverse effects. To clarify this issue, CD34 cells from human placental and umbilical cord blood were exposed under conditions of high-strength SMF in vitro. The high-strength SMF exposure system was comprised of a magnetic field generator with a helium-free superconducting magnet with built-in CO 2 incubator. Freshly prepared CD34 cells were exposed to a 5 tesla (T) SMF with the strongest magnetic field gradient (41.7 T/m) or a 10 T SMF without magnetic field gradient for 4 or 16 h. In the harvested cells after exposure to 10 T SMF for 16 h, a significant increase of hematopoietic progenitors in the total burst-forming unit erythroid- and megakaryocytic progenitor cells-derived colony formation was observed, thus producing 1.72- and 1.77-fold higher than the control, respectively. Furthermore, early hematopoiesis-related and cell cycle-related genes were found to be significantly up-regulated by exposure to SMF. These results suggest that the 10 T SMF exposure may change gene expressions and result in the specific enhancement of megakaryocytic/erythroid progenitor (MEP) differentiation from pluripotent hematopoietic stem cells and/or the proliferation of bipotent MEP. Bioelectromagnetics 30:280–285, 2009. ß 2009 Wiley-Liss, Inc. Key words: static magnetic fields; CD34 cells; hematopoietic progenitor cells; megakaryocytic/ erythroid hematopoiesis; MRI INTRODUCTION Man-made static magnetic fields (SMF) are used in research and in medical applications such as mag- netic resonance imaging (MRI) which provides three- dimensional images of the brain and other soft tissues. Scanned patients and machine operators can therefore be exposed to very high-strength SMF. The biological response after exposure to high-strength SMF has recently been widely discussed from the perspective of possible health benefits as well as potential adverse effects. Currently, stronger SMF up to 9.4 T are used for whole-body scanning to obtain higher resolution imaging in research applications [Sosnovik et al., 2007]. Guidelines for patient exposure to MRI are given by the U.S. Food and Drug Administration, International Electrotechnical Commission, National Radiological Protection Board and International Commission on Non-Ionizing Radiation Protection [Rockville, 1982; IEC 60601-2-33, 2002; Kanal et al., 2002; International Commission on Non-Ionizing Radiation Protection, 2004]. Despite these guidelines and the study of various biological effects induced by a high-strength SMF [Miyakoshi, 2005], there are still important safety issues regarding such exposure. The hematopoietic system is sensitive to extracellular oxidative stresses, such as DOI: 10.1002/bem.20480 Published online 24 February 2009 in Wiley InterScience (www.interscience.wiley.com). Received for review 2 July 2008; Final revision received 11 November 2008 Contract grant sponsor: Fund for the promotion of international scientific research (Hirosaki, Aomori). *Correspondence to: Ikuo Kashiwakura, Department of Radiologi- cal Life Sciences, Division of Medical Life Sciences, Hirosaki University Graduate School of Health Sciences, 66-1 Hon-cho, Hirosaki 036-8564, Japan. E-mail: ikashi@cc.hirosaki-u.ac.jp Bioelectromagnetics30:280 – 285(2009) ß 2009Wiley-Liss,Inc.