, 1999 and Galati et al., 2002). These phenoxyl radicals may be sufficiently reactive to co-oxidise NADH to NAD , which in turn can reduce O2 to O2 . The flavonoid derivatives containing a catechol ring, such as quercetin and fisetin, can oxidise NADH without oxygen uptake, suggesting that NADH undergoes a two-electron oxidation by the o-quinone product ( Constantin and Bracht, 2008). This bioactivation of RLX in the intact liver requests the

presence of a source of H2O2, NADH, and an enzyme acting similarly to horseradish peroxidase in the in vitro systems. The H2O2 that is required for the pro-oxidant effect of RLX in intact livers can be provided by both mitochondrial and peroxisomal fatty acid oxidation as it was clearly demonstrated ( Fig. 3). The peroxidase activity, SRT1720 in vivo on the other hand, was possibly mediated by the functional catalase-peroxidases, which, in the presence of a suitable electron donor and low levels of H2O2, have been shown to act as peroxidases ( Chelikani et al., 2004). It was also reported that raloxifene as

well as estradiol and other SERMs are metabolized to catechols derivatives and further to electrophilic o-quinones in rat liver microssomes (Yu et al., 2004 and Michalsen et al., 2012). It is likely that this metabolization also contributed to bioactivation of raloxifene in the perfused liver from both the CON and OVX rats. Apparently, the bioactive derivatives of raloxifene seem to be promptly neutralised by reacting with Cabozantinib the NADH produced by cell metabolism. This reaction, however, caused a disturbance in the redox potential of the NADH/NAD+ couple. In addition to changes in the fatty acid oxidation, other important metabolic processes that are modulated by the NADH/NAD+ redox potential may be altered by RLX, including glycolysis Thiamet G and gluconeogenesis (Kobayashi and Neely, 1979 and Kraus-Friedmann and Feng, 1996). It should be also

mentioned that the o-quinones can covalently modifying DNA and cellular proteins, a property that has been implicated in the carcinogenic action of some SERMs (Bolton et al., 2004). It appears likely that the effects of RLX reported here in the perfused livers may occur during the administration of therapeutic doses of RLX. Raloxifene was active in the perfused livers at a concentration of 25 μM and in isolated organelles at concentrations between 2.5 and 25 μM. Raloxifene has been shown to undergo extensive first-pass metabolism in the liver to glucuronide conjugates, resulting in an absolute bioavailability of nearly 1–2% (Hochner-Celnikier, 1999). A portal concentration of 25 μM would lead, in principle, to a systemic concentration of 0.25–0.5 μM. The maximal plasma concentration of RLX in healthy post-menopausal women has been reported to reach 0.18–2.87 μM following single or multiple oral dose administrations, respectively (Hochner-Celnikier, 1999).