The effect of Nrf2 activators tBHQ and 4-octyl itaconate on the nucleus pulposus cell degeneration

The present study aimed to investigate the impact of two Nrf2 agonists, tBHQ and 4-Octyl Itaconate, on nucleus pulposus (NP) degeneration and explore the underlying mechanism.

We isolated the NP cells from the disc tissue of disc herniation patients. NP cells were pretreated with an adequate dose of tBHQ, Itaconate, or the mixture of them, and then subjected to the Lipopolysaccharides (LPS) stimulation to induce degeneration. Besides, the Nrf2 gene silenced NP cells were also used as a comparison. Moreover, the LPS-treated NP cells were also cultured in the mix of tBHQ and Itaconate to determine whether the agonists affected reverse degeneration.

LPS treatment suppressed Nrf2 expression and induced the NP cell degeneration with a decrease of cell viability and collagen II expression, an increase of reactive oxygen species (ROS) production, inflammatory cytokine accumulation (IL-1β, TNF-α), and apoptosis (Caspase3, Caspase8). However, tBHQ or Itaconate pretreated NP cells contained a higher level of Nrf2 protein and alleviated the negative effect caused by LPS, which was abolished with the silencing of Nrf2. Additionally, tBHQ showed a better ability to suppress ROS than Itaconate. Meanwhile, Itaconate inhibited a higher amount of IL-1β and TNF-α than tBHQ. Interestingly, when NP cells were pretreated with both tBHQ and Itaconate, the result indicated an excellent anti-ROS and anti-inflammatory peculiarity. Furthermore, when NP cells suffered from LPS first and then treated with the agonist, the anti-ROS and anti-inflammatory effects remained. However, the cell viability, collagen II, and apoptotic degree were not improved.

Both tBHQ and Itaconate effectively prevent NP cells from degeneration through anti-ROS and anti-inflammation, and the combined use of them may have better effects. But in comparison, their impact on reversing NP cell degeneration has yet to be proven.