Cytotoxicity of Air Pollutant 9,10-Phenanthrenequinone: Role of Reactive Oxygen Species and Redox Signaling

Table 1

Major 9,10-phenanthraquinone studies and mechanisms of action.

Source	Concentrations/Doses of 9,10-PQ	Models (in vitro/in vivo)	Results/ mechanisms of action
Muraki et al. (2017) [62]	0.1–30 μM	Human embryonic kidney (HEK) cells and alveolar A549 cells	The results showed that 9,10‐PQ activated human TRPA1 via critical cysteine residues at 621 and 665 in the N‐terminus of the channel.
Asahi et al. (2014) [63]	50 mg/kg for male rat	Urine samples from Male rats and human	In rat urine samples following 9,10-PQ exposure, the monoglucuronide of 9,10-dihydroxyphenanthrene (9,10-PQHG) was found to be a major metabolite. 9,10-PQHG also present in human urine.
Hatae et al. (2013) [43]	10μM	HCT-116 colon tumor cells and HL-60 promyelocytic leukemia cells	Effects of orthoquinone moiety in 9,10-phenanthrenequinone on apoptosis were studied in HCT-116 and HL-60 cells. Results showed that the loss of the cis-orthoquinone unit in 9,10-PQ abrogated its ability to induce apoptosis in HCT-116 and HL-60 cells suggesting that cis-orthoquinine is an essential unit for 9,10-PQ to induce tumor cells apoptosis
Koizumi et al. (2013) [64]	10μM or 100μM	In Vitro Enzyme reaction	Redox cycling of 9,10-PQ in the presence of dihydrolipoic acid can cause oxidative damage of Cu, ZnSOD, which are associated with decreased enzyme activity.
Toyooka et al. (2012) [45]	0-25μM	A549 and MCF7 cell lines	In low NQO1-expressing cells, N-acetyl-L-cysteine (NAC) significantly enhanced 9,10-PQ-mediated cytotoxicity and the formation of DNA double-strand breaks with phosphorylation of histone H2AX. In contrast, 9,10-PQ-mediated cytotoxicity and genotoxicity were suppressed in presence of NAC in high NQO1-expressing human adenocarcinoma cell lines, A549 and MCF7. The results suggested that dual effects of NAC on 9,10-PQ-mediated cytotoxicity and genotoxicity are dependent on the NQO1 activity
Sugimoto et al. (2005) [65]	5-30μM	A549 human pulmonary epithelial cells	9,10-PQ induced apoptosis in A549 cells and the LC50 is ~7μM. Furthermore, 9,10-PQ induced the formation of hydroxyl radical in the presence of iron, NADPH, and P450 reductase in A549 cells. Chelating iron provided protection against the PQ-induced cytotoxicity. Treatment of A549 cells with PQ caused a decrease in levels of Cu,Zn–superoxide dismutase (Cu,Zn–SOD) and heme oxygenase-1 (HO-1) indicating that 9,10-PQ exerted oxidative stress in human A549 cells via iron-mediated oxidative damage with down-regulation of Cu, Zn-SOD.
Rodriguez et al. (2008) [49]	Aerobic conditions: 2.5-20μM; Anaerobic conditions: 20-50μM	yeast Saccharomyces cerevisiae	9,10 PQ can inhibit yeast S. cerevisiae growth under both aerobic and anaerobic conditions. However, 9,10 PQ induced DNA deletions and point mutations only in the presence of oxygen, not anaerobic conditions.
Taguchi et al. (2007) [66]	1-20μM	A549 human pulmonary epithelial cells	The results showed that PQH2 is the product of an NADPH-dependent two-electron reduction of 9,10-PQ. NADPH-dependent enzymes such as the AKR1C isozyme can mediate the two-electron reduction of 9,10-PQ to PQH2 resulting in redox cycling with 9,10-PQ, which is associated with oxidative protein damage
Peters et al. (2007) [67]	0-100μM	JEG-3 trophoblast cell line	9,10-PQ induced a concentration-dependent decline in Alamar Blue (AB), suggesting an impairment to energy metabolism. 9,10-PQ-mediated cytotoxicity was dramatically enhanced by the addition of copper.
Milko et al. (2009) [68]	TSQ Classic mass spectrometer with a QOQ configuration chemical reaction, 9,10-PQ as a ligand	Gas-phase model complexes [(PQ)FeCl(CH(3)O)](+), [(phen)FeCl(CH(3)O)](+), and [(PQ)(phen)FeCl(CH(3)O)](+)	The results showed that there is an interaction between iron(III) and phenanthraquinone in the isolated complexes in the gas phase, which is is driven by the reduction of iron(III) to iron(II) and 9,10-phenanthraquinone to the semihydroquinone radical or semiquinolate.
Hiyoshi et al. (2005) [69]	0.01 nmole/animal	Male ICR mice	Administration of 9,10-PQ (2.1 ng/animal) via intratracheal route dramatically increased allergic airway inflammation in mice and allergen-specific production of IgG1 and IgE.
Matsunag et al. (2008) [50]	1-10μM	human acute T-lymphoblastic leukemia MOLT-4 cells	9,10-PQ generated ROS, depleted cellular glutathione and trigged apoptosis signaling including mitochondrial membrane dysfunction and activation of caspases and poly(ADP-ribose) polymerase. 9,10-PQ-mediated ROS generation and cytotoxicity were increased in an XR-transformed cell line. Furthermore 9,10-PQ-induced cell death was partially inhibited when cells were pretreated with XR-specific inhibitors followed by 9,10-PQ exposure. These results suggest that -Xylulose reductase is critically involved in 9,10-phenanthrenequinone-induced apoptosis in human T lymphoma cells
KUMAGAI et al. (2001) [53]	In vitro (0.15-5 μM), in vivo (0.36 mmole/kg body weight)	Bovine aortic endothelial cells; Wistar rats (8–10 wk old)	9,10-PQ was found to significantly inhibit nitric oxide (NO) formation in bovine aortic endothelial cells with an IC(50) value of 0.6 μM. 9,10-PQ also inhibited endothelium-dependent relaxation of rat aortic rings while the endothelium-independent relaxation by nitroglycerin was not affected. Furthermore, intraperitoneal injection of 9,10-PQ (0.36 mmol/kg) to rats elevated blood pressure, plasma levels of stable NO metabolites, nitrite/nitrate compared to control group. These results suggested that 9,10-PQ is a potent inhibitory action on eNOS activity resulting in inhibition of NO-mediated vasorelaxation and elevation of blood pressure.
Taguchi et al. (2008) [70]	1–50 μM	Mouse primary hepatocytes	Exposure of human pulmonary epithelial A549 cells to 9,10-PQ resulted in a time-dependent formation of 9,10-PQH2 (9,10-PQHG) and. UGT1A10 and UGT1A6 found to be particularly involved in 9,10-PQHG formation. In cell-free systems, 9,10-PQ while not 9,10-PQHG, showed a quick thiol oxidation and oxygen consumption in the presence of dithiothreitol.
Oginuma et al. (2005) [71]	10 μM	Pig heart cytosol	9,10-PQ was found to be a potent inhibitor for the 4-benzoylpyridine (4-BP) reduction. and pig heart carbonyl reductase plays a critical role in superoxide generation via redox cycling of 9,10-PQ
Prisby et al. (2005)[32]	5 μM for In Vitro principal nutrient artery studies	Female and male Fischer-344 (F-344) rats	9,10-PQ diminished endothelium-dependent vasodilation of PNA in 14- and 24-mo-old rats of both genders. However, there was no change in femoral PNA in 6-mo-old male rats, suggesting that ovarian hormones play important role in the vascular endothelium at this stage of development.