5-Caffeoylquinic acid ameliorates oxidative stress-mediated cell death via Nrf2 activation in hepatocytes

5-Caffeoylquinic acid (5-CQA) is one of the most abundant compounds found in natural foods including coffee.

We investigated whether 5-CQA had a cytoprotective effect through the NF-E2-related factor 2 (Nrf2)-antioxidant response element (ARE) signalling pathway.

Nrf2 activation in response to 5-CQA treatment at the concentration of 10-100 μM is evaluated by Western blotting of Nrf2 and ARE reporter gene assay as well as its target gene expression in HepG2 cells. Intracellular reactive oxygen species (ROS) and glutathione (GSH) levels were measured in the tert-butyl hydroperoxide-induced hepatocytes to examined cytoprotective effect of 5-CQA (10-100 μM). The specific role of 5-CQA on Nrf2 activation was examined using Nrf2 knockout cells or Nrf2 specific inhibitor, ML-385.

Nuclear translocation of Nrf2 is increased by 5-CQA in HepG2 cells which peaked at 6 h. Consequently, 5-CQA significantly increases the ARE reporter gene activity and downstream antioxidant proteins, including glutamate cysteine ligase (GCL), hemeoxygenase-1 (HO-1), NAD(P)H quinone oxidoreductase 1, and Sestrin2. Nrf2 deficiency or inhibition completely antagonized ability of 5-CQA to induce HO-1 and GCL expression. Cells pre-treated with 5-CQA were rescued from tert-butyl hydroperoxide-induced ROS production and GSH depletion. Nrf2 activation by 5-CQA was due to increased phosphorylation of MAPKs, AMPK and PKCδ.

Taken together, our results demonstrate that as a novel Nrf2 activator, 5-CQA, may be a promising candidate against oxidative stress-mediated liver injury. Additional efforts are needed to assess 5-CQA, as a potential therapeutic in liver diseases in vivo and in humans.