Short-term exposure to dioxin impairs bone tissue in male rats P. Monica Lind a, * , Carolina Wejheden a , Rebecca Lundberg a , Pedro Alvarez-Lloret b , Sanne A.B. Hermsen a , Alejandro B. Rodriguez-Navarro b , Sune Larsson c , Agneta Rannug d a Institute of Environmental Medicine, Division of Biochemical Toxicology, Karolinska Institutet, Nobels väg 13, plan 3, Box 210, S-171 77 Stockholm, Sweden b Departamento de Mineralogía y Petrología, Facultad de Ciencias, Universidad de Granada, Avenida Fuentenueva s/n, 18071 Granada, Spain c Department of Surgical Sciences, Orthopaedics, Uppsala University, Sweden d Institute of Environmental Medicine, Division of Work Environment Toxicology, Karolinska Institutet, Box 210, S-171 77 Stockholm, Sweden article info Article history: Received 24 June 2008 Received in revised form 1 December 2008 Accepted 14 December 2008 Available online 18 January 2009 Keywords: Rodents TCDD PINP Mineralization Bone toxicity AhR (Ah receptor) abstract Chronic and sub-chronic studies in rats have previously shown that dioxin-like compounds impair the bone tissue homeostasis. In the present study, tibiae and serum were analyzed to study possible effects of short term dioxin exposure on rats. Two month old (ca. 200 g) male rats were injected with 50 lg 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) kg 1 bw and tibiae were excised 5 d following the exposure. Bone composition, dimensions and strength were analyzed by pQCT and three-point bending test on tibiae. In addition, detailed bone composition was analyzed by optical emission spectroscopy (ICP-OES) and Fourier transform infrared spectrometry (FTIR). Analysis of the serum bone biomarkers procollagen type-I N-terminal propeptide (PINP) and carboxyterminal cross linking teleopeptide (CTX) were also per- formed. pQCT-results showed alterations in the metaphysis, with a significant decrease in trabecular bone cross-sectional area (19%, p < 0.05) and a significant increase in total bone mineral density (+7%, p < 0.05) in TCDD-exposed rats. Analyses of the bones by ICP-OES and FTIR showed that bones from exposed rats had a higher relative proportion of crystalline phosphate (+13% for a1080 and +11% for a1113, p < 0.05) and lower acid phosphate content (22% for a1145, p < 0.05), resembling the composi- tion of more mature bones. Serum analysis showed that the bone formation marker PINP was decreased (37%, p < 0.05) and that the bone resorption marker CTX was increased (+14%, p < 0.05) indicating a net loss of bone tissue. In conclusion, 5 d of exposure to TCDD was sufficient to negatively affect bone tissue in male rats. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Dioxins are widespread pollutants which are found virtually everywhere in our environment in animals as well as in plants. Dioxins have never been commercially produced, but they are formed during waste incineration and as a contaminant during the production of some herbicides. These compounds are lipophilic and bioaccumulate and biomagnify in the food chain. In most stud- ies, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is used as the pro- totype compound when studying effects of dioxins. Studies on humans and on rodents show that dioxins cause a wide range of toxic effects, including impaired reproduction and cancer (WHO- ECEH/IPCS, 2000). Previous studies show that sub-chronic expo- sure to dioxins and dioxin-like compounds cause developmental bone and dental effects at low maternal doses (Miettinen et al., 2005; Alaluusua and Lukinmaa, 2006). Moreover, in experimental studies at higher doses, dioxin-like compounds have been shown to induce adverse effects on bone tissue composition and dimen- sions (Lind et al., 1999, 2004; Jämsa et al., 2001; Hermsen et al., 2008). Normal healthy bone is constantly being renewed through the continuous removal of bone and the subsequent replacement by synthesis of new bone matrix, followed by its mineralization. This so-called bone remodelling is under strict and complex regulation by multiple systemic hormonal factors and local acting factors. Persistent organic pollutants (POPs), such as dioxins and dioxin- like compounds may act as endocrine disrupting compounds and interfere with the homeostasis of bone tissue. The mechanisms behind TCDD-induced bone toxicity have been investigated in a few in vitro studies. These studies indicate that primarily the osteoblasts are affected. Studies on primary rat oste- oblasts exposed to TCDD showed that TCDD interferes with differ- entiation but not with the proliferation of these cells (Gierthy et al., 1994). A recent in vitro study showed that TCDD down-regulates the expression of osteopontin (OPN) in an osteoblast-like rat cell line, UMR-106 (Wejheden et al., 2006). OPN is a protein that has many effects in bone, i.e. it promotes attachment of the bone cells 0045-6535/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2008.12.024 * Corresponding author. Tel.: +46 8 524 87525; fax: +46 8 343849. E-mail address: Monica.Lind@ki.se (P.M. Lind). Chemosphere 75 (2009) 680–684 Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere