Redox cycling of 9,10-phenanthraquinone to cause oxidative stress is terminated through its monoglucuronide conjugation in human pulmonary epithelial A549 cells.
9,10-Phenanthraquinone (PQ), a component of airborne particulate matter, causes marked cellular protein oxidation and cytotoxicity through a two-electron reduction to 9,10-dihydroxyphenanthrene (PQH2), which is associated with the propagation of reactive oxygen species (K. Taguchi et al., Free Radic. Biol. Med. 43:789-799, 2007). In the present study, we explored a biotransformation pathway for the detoxification of PQ. Exposure of human pulmonary epithelial A549 cells to PQ resulted in a time-dependent appearance of an unknown metabolite in the medium that was identified as the monoglucuronide of PQH2 (PQHG). Whereas a variety of isozymes of uridine 5'-diphosphate glucuronosyltransferase (UGTs) are responsible for PQHG formation, UGT1A10 and UGT1A6 were particularly effective catalysts for glucuronide conjugation. In cell-free systems, PQ exhibited a rapid thiol oxidation and subsequent oxygen consumption in the presence of dithiothreitol, whereas PQHG did not. Unlike the parent compound, PQHG completely lost the ability to oxidize cellular proteins and cause cell death in A549 cells. In addition, deletion of the transcription factor Nrf2 decreased PQHG formation and increased PQ-mediated toxicity of mouse primary hepatocytes. Thus, we conclude that PQHG is a metabolite of PQ, generated through PQH2, that terminates its redox cycling and transports it to extracellular space.
Taguchi
Keiko
K
Doctoral Programs in Medical Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8575, Japan.
Shimada
Megumi
M
Fujii
Sayako
S
Sumi
Daigo
D
Pan
Xiaoqing
X
Yamano
Shigeru
S
Nishiyama
Takahito
T
Hiratsuka
Akira
A
Yamamoto
Masayuki
M
Cho
Arthur K
AK
Froines
John R
JR
Kumagai
Yoshito
Y
D000818:Animals; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D014453:Glucuronosyltransferase / Q000235:genetics / Q000378:metabolism; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D008658:Inactivation, Metabolic; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D000072019:Kelch-Like ECH-Associated Protein 1; D008168:Lung / Q000187:drug effects / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008813:Mice, Inbred ICR; D051267:NF-E2-Related Factor 2 / Q000235:genetics / Q000378:metabolism; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000187:drug effects*; D010101:Oxygen Consumption / Q000187:drug effects; D052638:Particulate Matter / Q000493:pharmacokinetics* / Q000633:toxicity; D010616:Phenanthrenes / Q000493:pharmacokinetics* / Q000633:toxicity; D013379:Substrate Specificity
D047908:Intracellular Signaling Peptides and Proteins; C431364:KEAP1 protein, human; D000072019:Kelch-Like ECH-Associated Protein 1; D051267:NF-E2-Related Factor 2; C495636:Nfe2l2 protein, mouse; D052638:Particulate Matter; D010616:Phenanthrenes; C005399:9,10-phenanthrenequinone; C110655:UDP-glucuronosyltransferase, UGT1A6; C476725:bilirubin uridine-diphosphoglucuronosyl transferase 1A10; D014453:Glucuronosyltransferase