Role of Nrf2 in protection against triptolide-induced toxicity in rat kidney cells

Triptolide is a major active ingredient of the Chinese herb Tripterygium wilfordii Hook f. (TWHF) and has been shown to possess multiple biological activities, such as anti-inflammatory, anti-fertility, anti-neoplastic and immunosuppressive activities. However, severe adverse effects, especially nephrotoxicity, limit its clinical use. Oxidative stress has been reported to be involved in triptolide-induced renal injury, but the existence of other mechanisms remains unclear. This study aimed to investigate whether NF-E2-related factor 2 (Nrf2), which is an antioxidant nuclear transcription factor, plays a protective role in defense against triptolide-induced toxicity in a normal rat kidney cell line (NRK-52E). Triptolide induced oxidative stress in NRK-52E cells by induction of reactive oxygen species (ROS) and depletion of glutathione (GSH), which resulted in a rapid increase in Nrf2 nuclear accumulation, as well as an induction of antioxidant response element (ARE)-driven genes. In addition, overexpression of Nrf2 protected against triptolide-induced cell death, whereas knockdown of Nrf2 by its specific small interfering RNA resulted in increased cytotoxicity. We also found that Nrf2 knockdown enhanced both the production of ROS and the depletion of GSH. Taken together, these results indicate that activation of Nrf2 plays a protective role against triptolide-induced cytotoxicity in NRK-52E cells through the counteraction of oxidative stress.