Excessive Reactive Oxygen Species and Exotic DNA Lesions as an Exploitable Liability

Superoxide dismutase activity enabled by a redox-active ligand rather than metal

Reactive oxygen species are integral to many physiological processes. Although their roles are still being elucidated, they seem to be linked to a variety of disorders and may represent promising drug targets. Mimics of superoxide dismutases, which catalyse the decomposition of O₂^•- to H₂O₂ and O₂, have traditionally used redox-active metals, which are toxic outside of a tightly coordinating ligand. Purely organic antioxidants have also been investigated but generally require stoichiometric, rather than catalytic, doses. Here, we show that a complex of the redox-inactive metal zinc(II) with a hexadentate ligand containing a redox-active quinol can catalytically degrade superoxide, as demonstrated by both reactivity assays and stopped-flow kinetics studies of direct reactions with O₂^•- and the zinc(II) complex. The observed superoxide dismutase catalysis has an important advantage over previously reported work in that it is hastened, rather than impeded, by the presence of phosphate, the concentration of which is high under physiological conditions.

TiO2 Photocatalysis in Aromatic "Redox Tag"-Guided Intermolecular Formal [2 + 2] Cycloadditions

Since the pioneering work by Macmillan, Yoon, and Stephenson, homogeneous photoredox catalysis has occupied a central place in new reaction development in the field of organic chemistry. While heterogeneous semiconductor photocatalysis has also been studied extensively, it has generally been recognized as a redox option in inorganic chemistry where such "photocatalysis" is most often used to catalyze carbon-carbon bond cleavage and not in organic chemistry where bond formation is usually the focal point. Herein, we demonstrate that titanium dioxide photocatalysis is a powerful redox option to construct carbon-carbon bonds by using intermolecular formal [2 + 2] cycloadditions as models. Synergy between excited electrons and holes generated upon irradiation is expected to promote the overall net redox neutral process. Key for the successful application is the use of a lithium perchlorate/nitromethane electrolyte solution, which exhibits remarkable Lewis acidity to facilitate the reactions of carbon-centered radical cations with carbon nucleophiles. The reaction mechanism is reasonably understood based on both intermolecular and intramolecular single electron transfer regulated by an aromatic "redox tag". Most of the reactions were completed in less than 30 min even in aqueous and/or aerobic conditions without the need for sacrificial reducing or oxidizing substrates generally required for homogeneous photoredox catalysis.

4β-Hydroxywithanolide E selectively induces oxidative DNA damage for selective killing of oral cancer cells

Reactive oxygen species (ROS) induction had been previously reported in 4β-hydroxywithanolide (4βHWE)-induced selective killing of oral cancer cells, but the mechanism involving ROS and the DNA damage effect remain unclear. This study explores the role of ROS and oxidative DNA damage of 4βHWE in the selective killing of oral cancer cells. Changes in cell viability, morphology, ROS, DNA double strand break (DSB) signaling (γH2AX foci in immunofluorescence and DSB signaling in western blotting), and oxidative DNA damage (8-oxo-2'deoxyguanosine [8-oxodG]) were detected in 4βHWE-treated oral cancer (Ca9-22) and/or normal (HGF-1) cells. 4βHWE decreased cell viability, changed cell morphology and induced ROS generation in oral cancer cells rather than oral normal cells, which were recovered by a free radical scavenger N-acetylcysteine (NAC). For immunofluorescence, 4βHWE also accumulated more of the DSB marker, γH2AX foci, in oral cancer cells than in oral normal cells. For western blotting, DSB signaling proteins such as γH2AX and MRN complex (MRE11, RAD50, and NBS1) were overexpressed in 4βHWE-treated oral cancer cells in different concentrations and treatment time. In the formamidopyrimidine-DNA glycolyase (Fpg)-based comet assay and 8-oxodG-based flow cytometry, the 8-oxodG expressions were higher in 4βHWE-treated oral cancer cells than in oral normal cells. All the 4βHWE-induced DSB and oxidative DNA damage to oral cancer cells were recovered by NAC pretreatment. Taken together, the 4βHWE selectively induced DSB and oxidative DNA damage for the ROS-mediated selective killing of oral cancer cells.

1,3-Dichloro-2-propanol evokes inflammation and apoptosis in BV-2 microglia via MAPKs and NF-κB signaling pathways mediated by reactive oxygen species

1,3-dichloro-2-propanol (1,3-DCP) is a widely concerned food processing contaminant which has been investigated for decades. While the neurotoxicity of 1,3-DCP and related mechanisms are still elusive. Herein, the effect of 1,3-DCP on neurotoxicity was investigated using BV-2 microglia cells. 1,3-DCP significantly decreased cell viability from 78.6% to 59.2% at doses between 2 and 20 mM. AO/EB and JC-1 staining indicated that 1,3-DCP induced apoptosis by means of the decrease of mitochondrial membrane potential. Meanwhile, western blot showed that 1,3-DCP stimulated inflammation of BV-2 cells through phosphorylation of MAPKs and activation of NF-κB pathways mediated by reactive oxygen species (ROS). Furthermore, the degree of inflammation and apoptosis has eased through MAPKs and NF-κB pathways with cells pretreated by N-acetylcysteine (NAC). Overall, these results presented here suggested that 1,3-DCP has neurotoxic effect on BV-2 microglia mainly via MAPKs and NF-κB pathways mediated by ROS.

Alantolactone induces apoptosis, promotes STAT3 glutathionylation and enhances chemosensitivity of A549 lung adenocarcinoma cells to doxorubicin via oxidative stress

Alantolactone (ALT), a sesquiterpene lactone component of Inula helenium, has been reported to exert anticancer activity in various cancers. However, the cellular targets and underlying mechanism of anticancer activity of ALT in various cancers including lung cancer has not been fully defined. In the present study, we found that ALT effectively inhibits proliferation and triggers oxidative stress mediated-apoptosis in A549 lung adenocarcinoma cells by inducing ER stress and mitochondrial dysfunction. This ALT-mediated apoptosis was inhibited by NAC while diamide potentiated it. Moreover, ALT effectively suppressed both constitutive and inducible STAT3 activation, inhibited its translocation into nucleus and decreased its DNA binding activity. Further mechanistic study revealed that ALT abrogated STAT3 activation by promoting STAT3 glutathionylation. ROS scavenger NAC reverted ALT-mediated STAT3 glutathionylation and inhibition of STAT3 phosphorylation. Finally, ALT enhanced chemosensitivity of A549 cells to doxorubicin and reversed doxorubicin resistance in A549/DR cells by inhibiting STAT3 activation and P-glycoprotein expression and increasing intracellular accumulation of doxorubicin. Suppression of STAT3 activation by targeting ROS metabolism with ALT thus discloses a previously unrecognized mechanism underlying the biological activity of ALT. Taken together; ALT induces oxidative stress-dependent apoptosis, inhibits STAT3 activation and augments doxorubicin toxicity in A549 lung cancer cells. These findings provide an in-depth insight into the molecular mechanism of ALT in the treatment of lung cancer.