Mitochondriotropic antioxidant based on caffeic acid AntiOxCIN4 activates Nrf2-dependent antioxidant defenses and quality control mechanisms to antagonize oxidative stress-induced cell damage

Abstract

Mitochondria are key organelles involved in cellular survival, differentiation, and death induction. In this regard, mitochondrial morphology and/or function alterations are involved in stress-induced adaptive pathways, priming mitochondria for mitophagy or apoptosis induction. We have previously shown that the mitochondriotropic antioxidant AntiOxCIN₄ (100 μM; 48 h) presented significant cytoprotective effect without affecting the viability of human hepatoma-derived (HepG2) cells. Moreover, AntiOxCIN₄ (12.5 μM; 72 h) caused a mild increase of reactive oxygen species (ROS) levels without toxicity to primary human skin fibroblasts (PHSF). As Nrf2 is a master regulator of the oxidative stress response inducing antioxidant-encoding gene expression, we hypothesized that AntiOxCIN₄ could increase the resistance of human hepatoma-derived HepG2 to oxidative stress by Nrf2-dependent mechanisms, in a process mediated by mitochondrial ROS (mtROS). Here we showed that after an initial decrease in oxygen consumption paralleled by a moderate increase in superoxide anion levels, AntiOxCIN₄ led to a time-dependent Nrf2 translocation to the nucleus. This was followed later by a 1.5-fold increase in basal respiration and a 1.2-fold increase in extracellular acidification. AntiOxCIN₄ treatment enhanced mitochondrial quality by triggering the clearance of defective organelles by autophagy and/or mitophagy, coupled with increased mitochondrial biogenesis. AntiOxCIN₄ also up-regulated the cellular antioxidant defense system. AntiOxCIN₄ seems to have the ability to maintain hepatocyte redox homeostasis, regulating the electrophilic/nucleophilic tone, and preserve cellular physiological functions. The obtained data open a new avenue to explore the effects of AntiOxCIN₄ in the context of preserving hepatic mitochondrial function in disorders, such as NASH/NAFLD and type II diabetes.

Keywords: Antioxidant defenses; Autophagy; Caffeic acid; Dietary antioxidants; Mitochondria; Mitochondria-targeted antioxidants; Nrf2.