Research Report Induction of microglial reactive oxygen species production by the organochlorinated pesticide dieldrin Haoyu Mao a , Xi Fang a , Katon M. Floyd a , Jeanette E. Polcz a , Ping Zhang a , Bin Liu a,b, ⁎ a Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville, FL 32610, USA b The McKnight Brain Institute, University of Florida, Gainesville, FL 32610, USA ARTICLE INFO ABSTRACT Article history: Accepted 6 October 2007 Available online 18 October 2007 Exposure to pesticides has been speculated to contribute to the development of sporadic Parkinson's disease (PD) characterized by a progressive degeneration of the nigrostriatal dopaminergic pathway. Activation of brain microglia that produce various neurotoxic factors including cytokines and reactive oxygen species (ROS) has been increasingly associated with dopaminergic neurodegeneration induced by various toxicants. Dieldrin, a highly persistent organochlorinated pesticide found enriched in the substantia nigra of some postmortem PD brains, has been shown to be toxic to dopamine neurons. In this study, we set out to determine the effect of dieldrin on the production of ROS and the underlying mechanism of action in murine microglia. Treatment of microglial cells with 0.1 nM to 1 μM dieldrin for 24 h resulted in a concentration-dependent generation of ROS. The dieldrin- induced microglial ROS generation was time-dependent in that significant ROS production was observed in cells 12–24 h, but not 6 h after dieldrin treatment. Furthermore, the dieldrin- induced microglial ROS generation was significantly reduced by inhibitors of NADPH oxidase, gene transcription and protein synthesis. In addition to immortalized microglial cells, dieldrin induced a concentration-dependent ROS generation in primary microglia, but not in primary astroglia. These results demonstrate that nanomolar concentrations of dieldrin can stimulate microglia to produce ROS that may contribute to the degeneration of dopamine neurons known to be vulnerable to oxidative damage. These findings provide important information on the potential role of microglia in dieldrin-induced neurodegeneration in relevance to the development of idiopathic PD. © 2007 Elsevier B.V. All rights reserved. Keywords: Microglia Free radical Organochlorinated pesticide Activation Astrocyte 1. Introduction Environmental exposure to pesticides is a possible risk factor to the development of idiopathic Parkinson's disease (PD), a movement disorder resulting from the progressive destruction of the nigrostriatal dopaminergic pathway (Kamel et al., 2007; Liu et al., 2003). Multiple lines of evidence indicate that, among the various suspected pesticides, the organochlorinated pes- ticide (OCP) dieldrin may be a strong candidate that may con- tribute to PD development. First, the highly persistent and bio- BRAIN RESEARCH 1186 (2007) 267 – 274 ⁎ Corresponding author. University of Florida, Box 100487, Gainesville, FL 32610, USA. Fax: +1 352 273 7705. E-mail address: liu@cop.ufl.edu (B. Liu). URL: http://www.cop.ufl.edu/departments/PD/faculty/liu/index.htm (B. Liu). Abbreviations: DCF-DA, 2′,7′-dichlorofluorescein diacetate; DMEM, Dulbecco's modified Eagle's medium; DMEM/F12, DMEM/nutrient mixture F12 (1:1); DMSO, dimethyl sulfoxide; DPI, diphenylene iodonium; FBS, fetal bovine serum; HBSS, Hank's balanced salt solution; OCP, organochlorinated pesticide; PBS, phosphate-buffered saline; PD, Parkinson's disease; ROS, reactive oxygen species 0006-8993/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.brainres.2007.10.020 available at www.sciencedirect.com www.elsevier.com/locate/brainres