Toxicology Letters 195 (2010) 147–154 Contents lists available at ScienceDirect Toxicology Letters journal homepage: www.elsevier.com/locate/toxlet The effect of -naphthoflavone on the metabolism of amiodarone by hepatic and extra-hepatic microsomes Marwa E. Elsherbiny, Ayman O.S. El-Kadi, Dion R. Brocks ∗ Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2N8 article info Article history: Received 3 February 2010 Received in revised form 18 March 2010 Accepted 24 March 2010 Available online 1 April 2010 Keywords: Cytochrome P450 Amiodarone toxicity Gene expression CYP1A Polycyclic aromatic hydrocarbons Induction abstract Amiodarone is a potent antiarrhythmic drug with several limiting side effects, some of which have been correlated with increased levels of its more toxic metabolite, desethylamiodarone. Elevated serum desethylamiodarone to amiodarone ratios are associated with a risk of amiodarone-induced pulmonary toxicity. Polycyclic aromatic hydrocarbons such as -naphthoflavone are known to increase desethy- lamiodarone levels in rat in vivo. In this article we investigated if this increase was solely due to increased formation as a result of cytochrome P450 (CYP) 1A1 and 1A2 induction in different rat hepatic and extra- hepatic tissues. Additionally, the effect of amiodarone treatment on CYP1A1 and 1A2 gene expression and activity was investigated. In rats, -naphthoflavone was found to increase desethylamiodarone forming activity in lung and kidney microsomes. Amiodarone increased -naphthoflavone mediated induction of CYP1A1 gene expression in liver, lung and kidney. However, there was no significant change in CYP1A activity. As expected, the data indicated that the increase in desethylamiodarone levels in vivo was partly due to increased formation through CYP1A1 induction, although increased formation was only evident in some extra-hepatic tissues. Amiodarone treatment did not affect basal or induced CYP1A activity. © 2010 Elsevier Ireland Ltd. All rights reserved. 1. Introduction Amiodarone (AM) is a benzofuran derivative commonly pre- scribed for the treatment of ventricular and supraventricular arrhythmias (Naccarelli et al., 2000; Piccini et al., 2009; Snider et al., 2009). It has a large volume of distribution, being exten- sively sequestered by tissues such as lung, liver and adipose tissues (Brien et al., 1987; Holt et al., 1983; Shayeganpour et al., 2008). Metabolic transformation in the liver is the main route for AM elim- ination (Fabre et al., 1993; Trivier et al., 1993). To date, there is evidence of several metabolites being formed from AM biotrans- formation (Ha et al., 2001; Young and Mehendale, 1986). The main circulating metabolite, however, is mono-N-desethylamiodarone (DEA), which is detectable at relatively high levels in serum and/or plasma and tissues of human and preclinical animal species (Brien et al., 1987; Elsherbiny and Brocks, 2010; Hamdy and Brocks, 2009; Kannan et al., 1989; Meng et al., 2001; Shayeganpour et al., 2008; Stark et al., 1991). Notably, DEA also possesses electrophysiolog- ical activity similar to that of its parent drug (Stark et al., 1991). Several cytochrome P450 (CYP) isoenzymes are involved in the bio- ∗ Corresponding author at: Faculty of Pharmacy and Pharmaceutical Sciences, 3118 Dentistry/Pharmacy Centre, University of Alberta, Edmonton, Alberta, Canada T6G 2N8. Tel.: +1 780 492 2953; fax: +1 780 492 1217. E-mail address: dbrocks@pharmacy.ualberta.ca (D.R. Brocks). transformation of AM to DEA. For example, CYP3A4, 1A1/2, 2D6 and 2C8 were found to be involved in DEA formation in human whereas CYP3A1/2, 1A1, 2C11 and 2D1 were found to mediate DEA formation in rat (Elsherbiny et al., 2008; Ohyama et al., 2000a; Shayeganpour et al., 2006). Despite the beneficial use of AM in the treatment of arrhyth- mias, AM use is sometimes discontinued because of some serious side effects. These adverse effects can involve liver, thyroid, skin, pancreas and lung (Batcher et al., 2007; Chen et al., 2007; Jarand et al., 2007; Puli et al., 2005). In several organs, DEA has been shown to be more toxic than AM. For example, DEA caused a decrease in the mitochondrial membrane potential and cell death in human and rat pulmonary alveolar epithelial cells at lower concentrations than those of AM (Bargout et al., 2000; Bolt et al., 2001). The concentra- tions in human alveolar epithelial cell lines (A549) that resulted in 50% cell death were recently reported to be 50 and 12 M for AM and DEA, respectively (Seki et al., 2008). Furthermore, this more potent cytotoxic effect of DEA was consistently observed in human hepatocellular carcinoma (HepG2) and immortalized thyrocytes cell line (SGHTL-34 cells) (Beddows et al., 1989; Waldhauser et al., 2006) with similar observations being documented in animal models such as the rat (Somani et al., 1990). Exposure to polycyclic aromatic hydrocarbons (PAH), potent CYP1A inducers, can lead to significant increases in the DEA lev- els in the plasma, liver, heart and lung tissues of AM treated rats (Elsherbiny and Brocks, 2010). Although these compounds are con- 0378-4274/$ – see front matter © 2010 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.toxlet.2010.03.019