Real time-quantitative polymerase chain reaction analysis of the anti-inflammatory effect of aqueous rooibos (Aspalathus linearis) extract on diesel exhaust particles-induced hepatic inflammation

Abstract

Air pollution has been implicated in the etiology of different pathological conditions in human. Though air pollution is heterogeneous in composition, most of its deleterious effects have been linked to the particulate matter (PM) component. In this study we used the real time-quantitative polymerase chain reaction (RT-qPCR)
method to evaluate the protective effect of aqueous rooibos (Aspalathus linearis) extract (RE) from the inflammation induced by diesel exhaust particles (DEP) in the liver of exposed Wistar rats. One group of wistar rats was exposed to DMSO and saline vehicles (control), another group was given RE (50 mg/kg) orally for 4 weeks. The third group was pre-treated with oral dose of 50 mg/kg RE for 2 weeks before concomitant exposure to 50 mg/kg RE orally and 0.7 mg/kg DEP subcutaneously for further 2 weeks. The fourth group was given 0.7 mg/kg DEP subcutaneously for 2 weeks. Rats were then sacrificed and liver tissue collected and stored at -80^oC for further analysis. Real time-quantitative polymerase chain reaction was used to analyse IL-8, IL-10, TNFα, NF-kB, IkB and IkKB gene expressions as indices of inflammation. Rooibos extract pre-treatment significantly (p<0.001) decreases the mRNA levels of IL-8 and TNFα induced by diesel exhaust particles exposure, but increased IL-10 mRNA level significantly (p<0.05). While rooibos extract pre-treatment caused significant (p<0.001) increase in IkB gene expression compared to diesel exhaust particles only, it did cause significant (p<0.05) decrease in NF-kB and IkKB mRNA levels. In conclusion, the results suggest that rooibos extract has the ability to mitigate against diesel exhaust particles-induced inflammation in hepatic tissue by a mechanism that may involve the suppression of the NF-kB signalling pathway.

Keywords: Inflammation; Diesel exhaust particles; Liver; Air pollution; Rooibos; Gene expression