The International Journal of Biochemistry & Cell Biology 36 (2004) 931–941 An investigation into the detoxification of microcystin-LR by the glutathione pathway in Balb/c mice Michelle M. Gehringer a,b,∗ , Enid G. Shephard c , Tim G. Downing b , Claudia Wiegand d , Brett A. Neilan a,e a School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney 2052, Australia b Department of Biochemistry and Microbiology, University of Port Elizabeth, P.O. Box 1600, Port Elizabeth 6000, South Africa c MRC/UCT Liver Research Centre, Groote Schuur Hospital, University of Cape Town, Old Main Building, Rondebosch, Cape Town, South Africa d Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 301, D-12587 Berlin, Germany e The Clive and Vera Ramaciotti Centre for Gene Function Analysis, University of New South Wales, Sydney 2052, Australia Received 29 July 2003; received in revised form 30 September 2003; accepted 13 October 2003 Abstract Toxin-producing cyanobacteria pose a world-wide health threat to humans and animals due to their increasing presence in both drinking and recreational waters. The predominant cyanotoxin, microcystin-LR (MCLR), targets the liver and its toxicity depends on the uptake and removal rates in the liver. The role of the glutathione detoxification pathway in protecting the liver from the effects of MCLR was investigated. Mice exposed to a single 75% LD 50 dose of pure MCLR were sacrificed at 8, 16, 24 and 32h post-exposure (pe). Toxin induced liver damage was observed 8 and 16h pe as evidenced by raised serum ALT and LDH levels, reduced glycogen levels and liver histology. A significant increase in lipid peroxidation was seen at 16h pe that decreased after 24 and 32 h pe, the time-points which showed significant increases in GPX activity. An increase in soluble GST activity was noted between 8 and 16 h pe, levels of total GSH increased at 24 h while oxidised glutathione increased throughout the investigation. The increase in activity of both GPX and GST corresponded with increased transcription of these enzymes, as well as the rate-limiting enzyme in GSH synthesis, -glutamyl transferase. In conclusion, this study confirms that an increase in GST activity is critical for the detoxification of MCLR, that this is regulated at the transcriptional level, and that exposure to MCLR induces the de novo synthesis of GSH. Finally, we report the involvement of GPX in the removal of MCLR-induced lipid hydroperoxides. © 2003 Elsevier Ltd. All rights reserved. Keywords: Cyanobacteria; Glutathione S-transferase; Glutathione peroxidase; Lipid peroxidation; Microarray Abbreviations: MCLR, microcystin-LR; GPX, glutathione per- oxidase; GSH, glutathione; GST, glutathione S-transferase; sGST, soluble GST; i.p., intraperitoneal; GSSG, oxidised GSH dimer; pe, post-exposure; ww, wet weight ∗ Corresponding author. Tel.: +61-2-9385-3235; fax: +61-2-9385-1591. E-mail addresses: mgehringer@unsw.edu.au, bcammg@upe.ac.za (M.M. Gehringer). 1. Introduction Cyanobacteria, specifically Microcystin aerugi- nosa, pose a threat to animal and human health by virtue of their ability to produce the hepatotoxic hep- tapeptide, microcystin (Codd, Ward, & Bell, 1997; Falconer, 2001). The reported incidences of animal and human exposure to microcystin (Codd et al., 1997; 1357-2725/$ – see front matter © 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.biocel.2003.10.012