Sulforaphane Cannot Protect Human Fibroblasts From Repeated, Short and Sublethal Treatments with Hydrogen Peroxide

Mechanisms underlying Nrf2 nuclear translocation by non-lethal levels of hydrogen peroxide: p38 MAPK-dependent neutral sphingomyelinase2 membrane trafficking and ceramide/PKCζ/CK2 signaling

Hydrogen peroxide is an aerobic metabolite playing a central role in redox signaling and oxidative stress. H₂O₂ could activate redox sensitive transcription factors, such as Nrf2, AP-1 and NF-κB by different manners. In some cells, treatment with non-lethal levels of H₂O₂ induces rapid activation of Nrf2, which upregulates expression of a set of genes involved in glutathione (GSH) synthesis and defenses against oxidative damage. It depends on two steps, the rapid translational activation of Nrf2 and facilitation of Nrf2 nuclear translocation. We review the molecular mechanisms by which H₂O₂ induces nuclear translocation of Nrf2 in cultured cells by highlighting the role of neutral sphingomyelinase 2 (nSMase2), a GSH sensor. H₂O₂ enters cells through aquaporin channels in the plasma membrane and is rapidly reduced to H₂O by GSH peroxidases to consume cellular GSH, resulting in nSMase2 activation to generate ceramide. H₂O₂ also activates p38 MAP kinase, which enhances transfer of nSMase2 from perinuclear regions to plasma membrane lipid rafts to accelerate ceramide generation. Low levels of ceramide activate PKCζ, which then activates casein kinase 2 (CK2). These protein kinases are able to phosphorylate Nrf2 to stabilize and activate it. Notably, Nrf2 also binds to caveolin-1 (Cav1), which protects Nrf2 from Keap1-mediated degradation and limits Nrf2 nuclear translocation. We propose that Cav1serves as a signaling hub for the control of H₂O₂-mediated phosphorylation of Nrf2 by kinases, which results in release of Nrf2 from Cav1 to facilitate nuclear translocation. In summary, H₂O₂ induces GSH depletion which is recovered by Nrf2 activation dependent on p38/nSMase2/ceramide signaling.

Antioxidant Activity of Compounds Isolated from Elaeagnus umbellata Promotes Human Gingival Fibroblast Well-Being

Four new triterpenoid bidesmosidic saponins (1-4) and a sesquiterpenoid glucoside (5), together with nine known phenolic compounds (6-14), were isolated from the fruits of Elaeagnus umbellata. Their structures were elucidated using 1D and 2D NMR spectroscopy and mass spectrometry data. The antioxidant capability of the isolated compounds was evaluated in human gingival fibroblasts. Compound 6 decreased ROS production and promoted cell proliferation. It also counteracted the cell cycle blockade induced by a low concentration of H2O2 decreasing the expression of p21 and CDKN2A (p16INK4A). Compound 6 decreased the expression of inflammatory cytokines (IL-6 and IL-8) in response to inflammatory stimuli, supporting its possible use in periodontitis lesions.

Knockdown of macrophage migration inhibitory factor (MIF), a novel target to protect neurons from parthanatos induced by simulated post-spinal cord injury oxidative stress

Parthanatos is a form of regulated cell death (RCD) that is closely linked to DNA damage, which is a common consequence of oxidative stress due to central nervous trauma, such as spinal cord injury (SCI). The mechanism by which apoptosis-inducing factor (AIF) mediates DNA strand breaks in parthanatos was not clear until the discovery of the nuclease function of MIF. A previous study suggested that observed results may not be reliable if the oxidative stress induced in cells observed under experimental pathological conditions does not accurately replicate the specific pathologies being studied. According to an earlier direct measurement of extracellular oxidative stress in a rat SCI model, post-SCI oxidative stress was approximately the same as exposure to 150 μM H₂O₂. However, this concentration has been reported as sublethal oxidative stress in other cell types related to senescence, apoptosis, and parthanatos. Using sublethal H₂O₂ concentrations to induce oxidative stress is equivocal. Also, different cell types have diverse tolerances and responses to oxidative stress, and, therefore, exposure to H₂O₂. To avoid these limitations, the present study explored the mechanism of neuronal death under this simulated post-SCI oxidative stress and determined the effects of MIF knockdown in parthanatos associated with SCI. Immunofluorescence and flow cytometry were used to reveal typical characteristics of parthanatos that were blocked by PARP-1 inhibitors but not caspase inhibitors. In addition to classic features like PARP-1 and caspase-3 cleavage that were absent, we determined that parthanatos instead of apoptosis played a major role in the cell death caused by oxidative stress following SCI. Flow cytometry analysis of cells transfected by adenovirus with MIF-shRNA then exposed to H₂O₂ showed a significant decrease in cell death for MIF knockdown cells, even after AIF nuclear translocation. The comet assay also displayed significantly fewer DNA strand breaks after MIF knockdown. This is the first study has verified that MIF knockdown enables to protect neurons from parthanatos under a simulated in vivo oxidative stress following SCI. It suggests that MIF knockdown is a promising therapy to rescue neurons suffering from oxidative stress-induced SCI pathology.