Oxidative modification of lipids and proteins in aniline-induced splenic toxicity

Our earlier studies with aniline suggested the involvement of oxidative str ess as an early toxic event in the spleen. In order to understand the statu s and consequences of the damaging oxidative reactions, especially during t he progression of characteristic splenic lesions, time-dependent subchronic studies were conducted in rats. Male Sprague-Dawley rats were treated with 65 mg/kg/day aniline in the drinking water, while control rats received dr inking water only. The animals were euthanized after 1, 2, or 3 months of a niline exposure. Total iron content was remarkably greater in the aniline-t reated rats than in age-matched controls. There were time-dependent increas es in splenic lipid peroxidation of aniline-treated rats. Malondialdehyde-p rotein adducts were quantitated by a competitive ELISA and showed greater c oncentrations in the spleens of aniline-treated rats, further substantiatin g our lipid peroxidation results. Protein oxidation in the spleens of anili ne-treated rats was also greater, with a maximum increase of similar to 76% at 3 months. Western blot analysis for oxidized proteins showed two distin ct protein bands at similar to 114 kD and similar to 69 kD in both post-nuc lear and mitochondrial fractions of the spleens. Furthermore, densitometric analysis of the blot showed increased band intensities of the oxidized pro teins in both these spleen fractions from aniline-treated rats, suggesting the susceptibility of these proteins to aniline-induced oxidative stress. T he most prominent morphological changes in the spleens of aniline-treated r ats included thickening of the capsule, and capsular cells with nuclear pro minence and hyperchromia indicative of capsular hyperplasia. These capsular changes and fibrosis of capsule, splenic trabeculae, and red pulp were not ed at all three time points after aniline exposure. Our studies thus sugges t that aniline-induced oxidative stress in the spleen is an ongoing event t hat leads to oxidative modifications of biomolecules. Such oxidative modifi cations, directly or indirectly, could contribute to the splenic toxicity l eading to deleterious consequences, including capsular hyperplasia and fibr osis, as observed in this study, and possibly tumorigenesis in chronic anil ine exposure conditions.