Up-regulation of transforming growth factor-β1 in the spleen of aniline-treated rats

Aniline exposure produces selective toxicity to the spleen, leading to a variety of sarcomas in rats following chronic exposure. Fibrosis appears to be an important preneoplastic lesion of the spleen. However, early molecular events leading to splenic fibrosis are not known. Earlier studies have shown that aniline exposure in rats leads to excessive deposition of iron and increased lipid peroxidation in the spleen, which may produce changes in the expression of fibrogenic cytokines, such as transforming growth factor-β1 (TGF-β1), leading to splenic fibrosis. Therefore, this study was designed to establish whether aniline exposure leads to induction/overexpression of TGF-β1 and association of such induction with lipid peroxidation (oxidative stress) in the spleen. To achieve this, male Sprague-Dawley rats were given 1 mmol/kg/day aniline hydrochloride in water by gavage for 7 days, while controls received water only. Aniline treatment resulted in significant increases in spleen weight (97%), spleen-to-body weight ratios (104%), and splenocyte population (25%). Malondialdehyde-protein adducts, quantitated by a competitive ELISA, showed a 56% increase in the spleen of aniline-treated rats. TGF-β1, measured in the supernatants of cultured splenocytes by an ELISA specific for TGF-β1, showed a significant increase (60%) in the total TGF-β1 from aniline-treated rats. These increases were further confirmed by Western blot analysis, which showed ∼2.5-fold increase in cell-associated TGF-β1 protein expression in aniline-treated rats. Furthermore, determination of TGF-β1 mRNA expression showed a 4-fold increase in the spleens of aniline-treated rats. These results suggest an association between formation of MDA-protein adducts and overexpression of TGF-β1 as a result of aniline insult, which together could promote splenic injury and fibrogenesis.