Activation of the Nrf2 response by intrinsic hepatotoxic drugs correlates with suppression of NF-kappaB activation and sensitizes toward TNFalpha-induced cytotoxicity

50 nM siRNA.

Drug-induced liver injury (DILI) is an important problem both in the clinic and in the development of new safer medicines. Two pivotal adaptation and survival responses to adverse drug reactions are oxidative stress and cytokine signaling based on the activation of the transcription factors Nrf2 and NF-kappaB, respectively. Here, we systematically investigated Nrf2 and NF-kappaB signaling upon DILI-related drug exposure. Transcriptomics analyses of 90 DILI compounds in primary human hepatocytes revealed that a strong Nrf2 activation is associated with a suppression of endogenous NF-kappaB activity. These responses were translated into quantitative high-content live-cell imaging of induction of a selective Nrf2 target, GFP-tagged Srxn1, and the altered nuclear translocation dynamics of a subunit of NF-kappaB, GFP-tagged p65, upon TNFR signaling induced by TNFalpha using HepG2 cells. Strong activation of GFP-Srxn1 expression by DILI compounds typically correlated with suppression of NF-kappaB nuclear translocation, yet reversely, activation of NF-kappaB by TNFalpha did not affect the Nrf2 response. DILI compounds that provided strong Nrf2 activation, including diclofenac, carbamazepine and ketoconazole, sensitized toward TNFalpha-mediated cytotoxicity. This was related to an adaptive primary protective response of Nrf2, since loss of Nrf2 enhanced this cytotoxic synergy with TNFalpha, while KEAP1 downregulation was cytoprotective. These data indicate that both Nrf2 and NF-kappaB signaling may be pivotal in the regulation of DILI. We propose that the NF-kappaB-inhibiting effects that coincide with a strong Nrf2 stress response likely sensitize liver cells to pro-apoptotic signaling cascades induced by intrinsic cytotoxic pro-inflammatory cytokines.