Rooibos tea (Aspalathus linearis) extract protects against air particulate matter induced hepatic oxidative stress in Nrf2-independent manner

Abstract

Diesel exhaust particles (DEP) are a typical example of air particulate matter generated into the environment from industrial, residential and vehicular diesel engines. Studies have implicated the induction of oxidative stress in the adverse health effect of DEP. In this study, the effect of aqueous rooibos extract (RE) on DEP-induced hepatic oxidative stress was examined and the role of Nrf2-regulation in this effect was evaluated. Wistar rats were divided into 4 groups of 5 rats/group and were administered 0.7 mg/kg DEP subcutaneously and 50 mg/kg RE orally. Group one was given vehicle (saline and DMSO), group two was administered with RE for 4 weeks, group three was given RE for 2 weeks followed by concomitant administration of RE and DEP for further 2 weeks and group four was given DEP twice a week at the last 2 weeks of treatment. Malondialdehyde (MDA), Conjugated dienes (CDs) and GSH levels were determined in the liver homogenate. AST and ALT activities were assayed in the serum and RT-qPCR was used to quantify the gene expression of Nrf2 and HO-1 in the liver. Results showed that RE pre-treatment significantly (p<0.001) decreased DEP-induced elevated serum AST and ALT levels, decreased DEP-induced MDA (p<0.001) and CDs (p<0.05) levels.DEP caused significant (p<0.05) decrease in GSH levels, which was reversed by rooibos extract pre-treatment. DEP also caused significant induction in Nrf2 and HO-1 mRNA levels. However, these inductions were significantly attenuated by RE. In summary, rooibos extract has the potential to protect against DEP-induced oxidative stress in hepatic tissues probably by a mechanism which may not involve activation of the Nrf2-dependent response.

Keywords: Oxidative stress; diesel exhaust particles; rooibos tea; hepatic tissue