Entamoeba invadens: Influence of 60 Hz magnetic fields on growth and differentiation Abraham O. Rodrı ´guez-De la Fuente a, * , J. Antonio Heredia-Rojas a,1 , Benito David Mata-Ca ´rdenas b,1 , Javier Vargas-Villarreal b,1 , Laura E. Rodrı ´guez-Flores c,2 , Isaı ´as Balderas-Candanosa d,2 , Juan M. Alcocer-Gonza ´lez a,1 a Subdireccio ´ n de Postgrado, Facultad de Ciencias Biolo ´ gicas, UANL, Serafı ´n Pen ˜a #909 Norte, Monterrey, N.L. Me ´xico, C.P. 64000, Mexico b Centro de investigacio ´ n Biome ´dica del Noreste, Instituto Mexicano del Seguro Social, Divisio ´ n de Biologı ´a Celular y Molecular, Administracio ´ n e correo No. 4 Apartado Postal 020, Colonia Independencia, Monterrey, N.L. Me ´xico, CP 64720, Mexico c Departamento de Patologı ´a, Facultad de Medicina, UANL, Serafı ´n Pen ˜a #909 Norte, Monterrey, N.L. Me ´xico, C.P. 64000, Mexico d Departamento de Ciencias Exactas y Desarrollo Humano, Facultad de Ciencias Biologicas, UANL, Serafı ´n Pen ˜a #909 Norte, Monterrey, N.L. Me ´ xico, C.P. 64000, Mexico Received 18 September 2007; received in revised form 27 December 2007; accepted 22 January 2008 Available online 2 February 2008 Abstract Exposure to extremely low-frequency (ELF) electromagnetic fields appears to result in a number of important biological changes. In the present study, we evaluated the effects of 60 Hz sinusoidal magnetic fields (MF) at magnetic flux densities of 1.0, 1.5 and 2.0 mT on growth and differentiation of the protozoan Entamoeba invadens. We demonstrated an inhibitory growth effect when trophozoite cultures were exposed to 1.5 and 2.0 mT. Furthermore, we found that there was not a synergistic effect in cultures co-exposed to MF and Met- ronidazole, a cytotoxic drug against amoebic cells. In addition, MF exposure inhibited the encystation process of E. invadens. Ó 2008 Elsevier Inc. All rights reserved. Index Descriptors and Abbreviations: Magnetic fields; Trophozoites; Cytotoxicity; Entamoeba 1. Introduction There are some studies that have tested the effects of extremely low-frequency magnetic fields (ELF-MF) on dif- ferent types of cells. Some have observed no effect, but an increasing amount of reports show that exposure to ELF- MF can produce a variety of alterations. On this regard, magnetic fields were reported to alter the rate of cell growth (Liboff et al., 1984; Scarfi et al., 1999; Heredia-Rojas et al., 2001), suppress the T-lymphocyte cytotoxicity (Lyle et al., 1991), increase the growth-related enzyme ornithine decar- boxylase (Byus et al., 1988), alter cell surface properties (Marron et al., 1988) and cause direct effects on DNA structure (DaSilva et al., 2000). On the basis of present data, most scientists support that ELF-MF interact with cells. Effects on different species of ciliates (Paramecium biaur- elia, Loxodes striatus, Tetrahymena thermophila) have been used as single cell models to study the effects of ELF-MF at 50 Hz and 0.5–2.0 mT on migration rate (Hemmersbach et al., 1997). Dihel et al. (1985) have demonstrated an increased cell division rate in Paramecium exposed to a 72 Hz pulsated electromagnetic field. Also static magnetic fields, have bioeffects on protozoans. Ripamonti et al. (1981) reported that exposure to a static magnetic field lengthens the extension phase of the life cycle of the ciliated 0014-4894/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.exppara.2008.01.006 * Corresponding author. Fax: +52 0181 83524245. E-mail addresses: abrrodriguez@fcb.uanl.mx, abrrodriguez@yahoo. com.mx (A.O. Rodrı ´guez-De la Fuente). 1 Fax: +52 0181 83524245. 2 Fax: +52 0181 83762813. www.elsevier.com/locate/yexpr Available online at www.sciencedirect.com Experimental Parasitology 119 (2008) 202–206