Effects of ischemia–reperfusion on the absorption and esterase metabolism of diltiazem in rat intestine Antonio J. Molina, Julio G. Prieto, Gracia Merino, Gracia Mendoza, Rebeca Real, Mivis M. Pulido, Ana I. Álvarez ⁎ Department of Physiology, University of Leon, Campus de Vegazana s/n, 24071 Leon, Spain Received 14 June 2006; accepted 21 September 2006 Abstract Intestinal ischemia–reperfusion (I/R) is a serious clinical condition that triggers a complex inflammatory response. Inflammatory processes affect some enzymatic systems related to intestinal drug metabolism and bioavailability. Diltiazem (DTZ) is a calcium channel blocker, which is extensively metabolised in the intestine by esterases and different CYP450 isoforms. The main biotransformation pathway of DTZ in rats is desacetylation by esterases. This study analysed the effect of I/R on intestinal absorption and metabolism of DTZ, focusing on esterase activity, through different methodologies, after 60 min of superior mesenteric artery occlusion and 30 min of reperfusion or sham surgical procedures. The rate of DTZ appearance in blood during in situ studies increased significantly in the I/R group (0.094 ± 0.014 10 - 5 cm/s vs 0.271 ± 0.110 10 - 5 cm/s) and the calculated metabolised fraction of DTZ decreased significantly, showing an important reduction in the desacetylase activity in the I/R group. These results were supported by microsomal incubations, where desacetylase activity was related to esterases by specific inhibition, using paraoxon and bis-nitrophenylphosphate, and also by studies in everted rings. DTZ metabolism was higher in the jejunum than in the ileum, the esterase activity being affected by I/R in both regions. The present findings suggest that I/R injury clearly affects the esterases' activity and modifies the amount of DTZ and its metabolites in blood during in situ perfusion. This modification of intestinal esterase activity could be important for the pharmacokinetic behaviour of other drugs and prodrugs after intestinal pathologies involving inflammation and oxidative stress. © 2006 Elsevier Inc. All rights reserved. Keywords: Ischemia–reperfusion; Intestine; Diltiazem; Esterases; Metabolism; Absorption; Rat Introduction Intestinal ischemia injury is an important clinical problem in several disorders (Haglund, 1994). Intestinal ischemia leads to depletion of cellular energy (Schneider et al., 1994), and accu- mulation of toxic metabolites, resulting in cell damage and death. Reperfusion exacerbates ischemia-induced mucosal in- jury via the synthesis of reactive oxygen species (ROS) (Park et al., 1990; Massberg and Messmer, 1998), which is connected to neutrophil infiltration and the release of inflammatory reac- tion mediators (Massberg and Messmer, 1998; Carden and Granger, 2000; Yasuhara, 2005). Intestinal mucosal lesions after ischemia and reperfusion (I/R) injury include: loss of activity in brush border enzymes (Yeh et al., 1998; Stallion et al., 2005), cellular death (necrosis and apoptosis) (Ikeda et al., 1998; Noda et al., 1998) and increase of intestinal permeability (Khanna et al., 2001). I/R injury of the intestine and other organs has also been related to a decrease in drug metabolism activity (Tamura et al., 1997; Ishikawa et al., 2002; Suzuki et al., 2004). The importance of intestinal drug absorption, transport and metabolism after oral administration for drug bioavailability has been documented for many compounds (Kolars et al., 1991; Krishna and Klotz, 1994; Paine et al., 1996; Redondo et al., 1999). Changes in drug bioavailability due to pathological conditions, mainly those presenting inflammatory reactions, are responsible for some adverse events due to drugs (ADEs) (Soons et al., 1992; McDonnell and Jacobs, 2002; Carcillo et al., 2003; Haas et al., 2003). The health care costs entailed by such cases are tremendous (Goettler et al., 1997; Lagnaoui et al., 2000) and are avoidable. Life Sciences 80 (2007) 397 – 407 www.elsevier.com/locate/lifescie ⁎ Corresponding author. Tel.: +34 987291265; fax: +34 987291267. E-mail address: dfiaaf@unileon.es (A.I. Álvarez). 0024-3205/$ - see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.lfs.2006.09.035