Detoxication of Structurally Diverse Polycyclic Aromatic Hydrocarbon (PAH) o-Quinones by Human Recombinant Catechol-O-methyltransferase (COMT) via O-Methylation of PAH Catechols

Abstract

Polycyclic aromatic hydrocarbons (PAH)2 are ubiquitous environmental pollutants that are products of fossil fuel combustion and found in tobacco smoke and are suspect lung carcinogens (1, 2). PAH are considered to be procarcinogens and require metabolic activation to elicit their deleterious effects. Benzo[a]pyrene (B[a]P) is a representative PAH and widely used to study the metabolic activation of PAH (3, 4).There are three major pathways for the activation of B[a]P. In the first pathway, P450 peroxidases catalyze the generation of radical cations (5) PAH o-quinones, produced by AKRs are electrophilic and highly reactive to endogenous nucleophiles. PAH o-quinones can readily form conjugates with cellular thiols to yield and GSH conjugates, leading to their elimination (12,13). PAH o-quinones can also react with DNA to form both stable and depurinating adducts, which may result in mutagenesis (14 -16). PAH o-quinones are also able to undergo nonenzymatic/enzymatic reduction to reform catechols at the expense of NADPH and establish futile redox cycles that amplify the generation of reactive oxygen species (ROS). ROS can cause DNA damage resulting in the formation of 7,8-dihydro-8-oxo-2Ј-deoxyguanosine (8-oxo-dGuo) lesions and can contribute to G to T transversions in ras and p53 (17,18). PAH o-quinones were found to be more mutagenic than diol-epoxides in an in vitro p53 mutagenesis assay provided they redox-cycled and a linear correlation was observed

Detoxication of Benzo[a]pyrene-7,8-dione by Sulfotransferases (SULTs) in Human Lung Cells

“…These studies will document which enzymes attenuate the ability of AKR products to form ROS that can lead to the mutagenic lesion 8-oxo-dGuo. Previously we have shown that PAH o-quinones are enzymatically redox-cycled at a robust rate by recombinant NQO1 and by AKRs themselves and that human COMT can O-methylate a series of PAH-catechols (21,26). In this study we identify SULT1A1 as the major isoform responsible for the formation of B[a]P-7,8-catechol-O-monosulfate based on catalytic efficiency and enzyme expression level in human lung cells.…”

“…In human lung adenocarcinoma (A549) cells with high constitutive expression of AKRs, the metabolic activation of B[a]P-7,8-trans-dihydrodiol to B[a]P-7,8-dione by AKRs led to the formation ROS and 8-oxo-dGuo adducts in cellular DNA, which were exacerbated by the presence of a catechol-O-methyl transferase (COMT) inhibitor (25). The contribution of COMT to detoxication of PAH o-quinone was confirmed by demonstrating that human recombinant COMT detoxified structurally diverse PAH o-quinones, including B[a]P-7,8-dione, via O-methylation of PAH catechols (26).…”

Potential Metabolic Activation of a Representative C2-Alkylated Polycyclic Aromatic Hydrocarbon 6-Ethylchrysene Associated with the Deepwater Horizon Oil Spill in Human Hepatoma (HepG2) Cells

“…24 Sulfotransferases (SULTs) and catechol-O-methyltransferase would be responsible for the formation of O-monomethyl-O-monosulfonated-catechols. 25,26 The SULTs that are expressed in human HepG2 cells and likely responsible for O-sulfonation are SULT1A1, 1A2, 1E1, and 2A1. 18 γ-Glutamyltranspeptidase, dipeptidase, and N -acetyl transferase would sequentially catalyze the degradation of a GSH-ortho-quinone conjugate to generate the NAC-ortho-quinone conjugate that was detected.…”

G-ProteinβγSubunit Dimers Modulate Kidney Repair after Ischemia-Reperfusion Injury in Rats

“…First, the metabolism of gallein may be higher in the kidney, leading to lower intracellular concentrations available for biologic activity. Gallein has a polycyclic catechol structure, which may be a prime target for chemical modification by enzymes such as catechol-O-methyltransferase (COMT) (Zhang et al, 2011). COMT is known to be highly expressed in the kidney, including the S3 segment of the proximal tubule (Meister et al, 1993), and the activity level of COMT is 5-to 8-fold higher in the kidney compared with the heart or brain (Myohanen et al, 2010).…”