Real-Time Imaging of Astrocyte Response to Quantum Dots: In Vivo Screening Model System for Biocompatibility of Nanoparticles Dusica Maysinger,* ,² Maik Behrendt, Me ´ lanie Lalancette-He ´ bert, and Jasna Kriz* ,‡ Department of Pharmacology and Therapeutics, McGill UniVersity, Montreal, Quebec, Canada, and Department of Anatomy and Physiology, Centre de Recherche du CHUL, Faculty of Medicine, LaVal UniVersity, Quebec, QC, Canada Received July 4, 2007 ABSTRACT Astrocytes are the principle macroglial brain cells. They are activated by different stressors and brain injuries. Quantum dots (QDs) can cause oxidative stress. This study shows a real-time imaging of primary cortical cultures and assessment of QD-induced activation of astrocytes in the brains of transgenic mice with the luciferase gene driven by the murine astrocyte promoter. This approach may be widely applicable for assessing the astroglia/tissue response to nanoparticles in live animals. Different types of fluorescent nanoparticles were thoroughly characterized in cell lines, but very few were tested in primary cultures and live animals. A number of laboratories, including ours, have explored the physicochemical properties of nanoparticles as drug delivery systems and as bioimaging tools. 1-4 Imaging of the whole animal using fluorescent micelles remains difficult because of limited micelle stability in complex biological media 5-6 and strong autofluorescence of tissues due to endogenous chromophores (e.g., collagens, porphyrins, and flavins). A new class of semiconductor-based nanoparticles (i.e., quantum dots) has recently emerged as a complementary imaging tool with superior photophysical properties, which can at least in part overcome the limitations of fluorescent dyes. 2,7,8 A broad range of nanoparticles were investigated in different cell lines in vitro. 7-10 A common observation in these studies was that reactive oxygen species (ROS) are formed. The consequences of ROS formation are different depending on the cell type, concentration, and duration of exposure to the QDs as well as several physical and chemical properties of nanoparticles. 11-15 Surface-modified quantum dots (QDs) with polyethylene glycol (PEG) were reported to be biocompatible in vitro. 16 The physical, chemical, and biological properties and availability of polyethylene glycol (PEG) made this polymer an attractive corona-forming candidate for micelles and quantum dots. 17-20 Micelles with PEG corona were studied quite extensively and PEG-QDs, e.g., QD 545 (green), QD 655 (orange), QD 705 (far red), and QD 805 (near infrared) are now commercially available and some of them have already been tested in vitro in keratinocytes, 16 but none have been used for real-time imaging in vivo. There are few reports on the distribution and pharmacokinetic properties 21-24 of other types of QDs. These studies show that cadmium selenide QDs are seques- tered in several organs after iv administration 22 including lymph nodes 25 and solid tumors. 17 The biocompatibility of intraparenchymaly administered QDs in live animals, especially after repeated imaging sessions, has not yet been reported. Approaches for an early and sensitive detection of glia and neuron responsiveness to nanoparticles or other nanomaterials are therefore needed. Astrocytes are the principle macroglial cell type in the brain and their activation is one of the key components of the cellular responses to stress and brain injuries. The passage from the quiescent to reactive astrocytes is associated with strong upregulation of the intermediate filament, glial fibril- lary acidic protein (GFAP) in glia. 26,27 GFAP upregulation is considered a surrogate marker of neuronal stress and brain inflammatory response. Current methods of astrocyte and microglia detection are mainly based on immunocytochem- istry. However, in recent years, imaging strategies employing * Corresponding authors. E-mail: dusica.maysinger@mcgill.ca (D.M.); Jasna.Kriz@crchul.ulaval.ca (J.K.). Telephone: (514) 398-4400 x0838 (D.M.); Telephone: (418) 654-2296 (J.K.). Fax: (514) 398-6690 (D.M.); Fax: (418) 654-2761 (J.K.). ² Department of Pharmacology and Therapeutics, Faculty of Medicine, McGill University, 3655 Promenade Sir-William-Osler, Room 1314, McIntyre Medical Science Building, Montreal, Quebec, Canada H3G 1Y6. ‡ Department of Anatomy and Physiology, Centre de recherche du CHUL, Faculty of Medicine, Laval University, Quebec, QC, Canada, G1V 4G2. NANO LETTERS 2007 Vol. 7, No. 8 2513-2520 10.1021/nl071611t CCC: $37.00 © 2007 American Chemical Society Published on Web 07/19/2007