br Materials and methods br Results br Discussion

Materials and methods
Results
Discussion NB has been shown to induce cancers in many tissues including the kidney, liver, and thyroid, following chronic inhalation in animals (Hsu et al., 2007). The available data indicate that a lager majority of studies on NB evaluate the effects of toxic chemical exposure for a shorter duration (Li et al., 2003b). However, the impact of long-term exposure to pollutants has not been sufficiently examined. The present study investigated the effects of chronic exposure to NB on hepatic histological parameters, the antioxidant defence system and CYP450 enzyme of drakes. Antioxidant defences were able to scavenge ROSs and prevent increased oxidative damage in the tissues. Certain toxic chemicals can induce redox cycling and can cause severe peroxidative damage to cell structure and function (Monteiro et al., 2006, Ballesteros et al., 2009). One of the important features of antioxidant enzymes is their altered activity under oxidative stress, and such a change can be an important hydrobromide australia to pollutant-induced stress (Ahmad et al., 2004, Morena et al., 2005). SOD plays an important role in the antioxidant system, intervening in the first transformation by dismuting the superoxide free radicals into reactive forms of oxygen (Monferran et al., 2008). With the increasing concentration of NB, a strong inhibition of SOD activity was observed, which may be due to ROS overproduction and its relatively low antioxidant system. CAT is mainly located in peroxisomes and is responsible for the reduction of hydrogen peroxide into water and oxygen, produced from the metabolism of long-chain fatty acids (Stanic et al., 2006). According to previous studies, CAT activity always was negatively affected by certain toxic chemicals (Oruc et al., 2004; Kavitha and Rao, 2008). Similarly, in our study, we also found that CAT activity in the drake livers was inhibited after NB treatment and that the inhibition was stronger with increasing NB concentration. This stronger inhibition could be because of the flux in superoxide radicals, resulting in an increase in the hydrogen peroxide levels in the cell (Ahmad et al., 2000). GSH-Px catalyses the reduction of H2O2 and lipid peroxides at the expense of GSH (Uner et al., 2005). We observed a significant inhibition of GSH-Px activity in the livers of all treatmen groups after 40d. This test result could indicate that its antioxidant capacity was exceeded by the amount of hydro-peroxide products and reflect a possible failure of the antioxidant system in the livers of treated drake. LPO can be defined as the oxidative deterioration of cell membrane lipids and has been used extensively as a marker of oxidative stress (Sayeed et al., 2003). LPO is estimated by measuring the content of MDA. In this study, the MDA content in the liver in NB-treated groups was significantly higher compared to control. The over-accumulation of MDA can damage cells and trigger apoptosis (Kong et al., 2007). The CYP450 system is sensitive to the action of xenobiotic substances that may increase its activity, and thus, it has been proposed as a biomarker for pollutants (Tagliari et al., 2004). This system is also very important from a toxicological point of view (Henczova et al., 2008). For these two above-mentioned reasons, we decided to evaluate the CYP450 enzyme activities and CYP450 content of this system. In this study, NB exposure caused a condition-dependent increase in the CYP450 enzyme activities and CYP450 content. These results imply that NB induces CYP450 enzyme activities and increases the level of CYP450, which is in agreement with the reports of Harada and Omura (1980). However, the induction of CYP450 enzyme activities and increase in CYP450 level by NB exhibited intra-species varies even among individual drakes from the same treatment group. A wide difference between the control and the treatment groups makes the CYP450 enzyme activities and the CYP450 content in the liver potent biomarkers of the pollution caused by NB.