ORIGINAL ARTICLE Ochratoxin A impairs Nrf2-dependent gene expression in porcine kidney tubulus cells C. Boesch-Saadatmandi 1 , A. E. Wagner 1 , A. C. Graeser 1 , C. Hundhausen 1 , S. Wolffram 2 and G. Rimbach 1 1 Institute of Human Nutrition and Food Science, Christian Albrechts University Kiel, Kiel, Germany, and 2 Institute of Animal Nutrition and Physiology, Christian Albrechts University Kiel, Kiel, Germany Introduction Ochratoxin A (OTA) is an ubiquitous mycotoxin mostly produced by Aspergillus and Penicillium subspe- cies and present in feedstuffs (Bayman et al., 2002). Ochratoxin A exerts various toxic effects including nephro-, hepato-, terato-, immuno- and neurotoxic- ity (Kuiper-Goodman and Scott, 1989; Petzinger and Ziegler, 2000). The kidney is the main target tissue of OTA toxicity (Castegnaro et al., 1998; Luehe et al., 2003) and the chronic dietary exposure to OTA may be linked to the pathogenesis of nephropathy, a chronic tubulointerstitial kidney disease. Further- more, OTA is considered as a key factor of porcine nephropathy, which is endemic in Denmark (Elling and Moller, 1973; Krogh, 1987, 1992). Currently, the underlying mechanisms of OTA toxicity have not yet been fully elucidated. Several mechanisms have been proposed to explain OTA toxicity including inhibition of protein synthesis (Dirheimer and Creppy, 1991), mitchondrial activity alteration (Meisner and Chan, 1974) and oxidative stress (Petrik et al., 2003). Recently, it has been proposed that OTA may affect Nrf2 signal transduction pathways (Marin-Kuan et al., 2006; Cavin et al., 2007). However, so far, systematic studies in cell culture models also relevant to animal nutrition are missing. Under basal conditions, the transcription factor Nrf2 is bound to the cytosolic Kelch-like ECH-associated protein 1 (Keap1), a cysteine-rich Keywords ochratoxin A, Nrf2-dependent gene expression, kidney, pig Correspondence Prof. Dr. Gerald Rimbach, Institute of Human Nutrition and Food Science, Christian Albrechts University, Hermann-Rodewald- Strasse 6, Kiel, 24098, Germany. Tel: +49 431 880 2583; Fax: +49 431 880 2628; E-mail: rimbach@foodsci.uni-kiel.de Received: 29 February 2008; accepted: 28 April 2008 First published online: 10 June 2008 Summary The mycotoxin, ochratoxin A (OTA), which is produced by Aspergillus and Penicillium subspecies, is frequently present in feedstuffs. Ochratoxin A exhibits a wide range of toxic activities including nephrotoxicity. However, the underlying molecular mechanisms of OTA-induced cellu- lar nephrotoxicity have yet not been fully elucidated. Nrf2 is a basic leu- cine zipper transcriptional activator essential for the coordinated transcriptional induction of antioxidant and xenobiotic metabolizing enzymes in the kidney. Therefore, in the present study, the effects of OTA on the nuclear translocation and transactivation of the transcrip- tion factor Nrf2 as well as mRNA levels of Nrf2 target genes including glutathione-S-transferase and c-glutamylcysteinyl synthetase have been studied in cultured porcine kidney tubulus cells (LLC-PK1). Nrf2 was induced by sulforaphane, a well-known activator of this transcription factor. Ochratoxin A significantly decreased c-glutamylcysteinyl synthe- tase and glutathione-S-transferase mRNA levels in LLC-PK1 cells. Decreased mRNA levels of c-glutamylcysteinyl synthetase and glutathi- one-S-transferase were accompanied by a lowered nuclear translocation and transactivation of Nrf2. Furthermore, OTA also lowered Nrf2 mRNA levels. Current data indicate that OTA nephrotoxicity may be, at least partly, mediated by an Nrf2-dependent signal transduction pathway. DOI: 10.1111/j.1439-0396.2008.00838.x Journal of Animal Physiology and Animal Nutrition 93 (2009) 547–554 ª 2008 The Authors. Journal compilation ª 2008 Blackwell Verlag GmbH 547