Protective effects of oleanolic acid on oxidative stress and the expression of cytokines and collagen by the AKT/NF-κB pathway in silicotic rats

Oleanolic acid (OA), a natural pentacyclic triterpenoid, has been reported to have several benefits and medicinal properties. However, its protective effects against silica-induced lung injury and fibrosis remain to be elucidated. The aim of the present study was to investigate the effects of OA on oxidative stress, and the expression of cytokines and collagen in silicotic rats. Male rats were induced by intratracheal instillation of silicosis (250 mg/kg), with the exception of the control group (NS). The rats in the OA group were intragastrically administered with OA (60 mg/kg/d). The rats in the solvent control group were gavaged daily with 0.6% sodium carboxymethyl cellulose (10 ml/kg) solution for 56 consecutive days. The data showed that OA significantly attenuated the extent of silicosis fibrosis by histopathologic analysis of the lung tissues. In addition, oxidative stress activated by silica exposure, as evidenced by increasing of malondialdehyde content, and activities of superoxide dismutase and glutathione peroxidase in the lung, was regulated by treatment with OA. Furthermore, enzyme-linked immunosorbent assay analysis showed that OA significantly decreased the levels of tumor necrosis factor-a and transforming growth factor-alpha 1. Immunohistochemistry analysis showed that OA significantly decreased collagen types I and III. In investigating the mechanisms underlying the action of OA, it was found that OA decreased the level of phosphorylated AKT1, which in turn inactivated the transcriptional of nuclear factor (NF)-kappa B in the development and progress of silicosis. In conclusion, these results suggested that the protective effects of OA were due, at least in part, to its anti-oxidant activity and its ability to decrease the expression of cytokines and collagen by modulating the AKT/NF-kappa B pathway.