Reduction and Scavenging of Chemically Reactive Drug Metabolites by NAD(P)H:Quinone Oxidoreductase 1 and NRH:Quinone Oxidoreductase 2 and Variability in Hepatic Concentrations

Abstract

Detoxicating enzymes NAD(P)H:quinone oxidoreductase 1 (NQO1) and NRH:quinone oxidoreductase 2 (NQO2) catalyze the two-electron reduction of quinone-like compounds. The protective role of the polymorphic NQO1 and NQO2 enzymes is especially of interest in the liver as the major site of drug bioactivation to chemically reactive drug metabolites. In the current study, we quantified the concentrations of NQO1 and NQO2 in 20 human liver donors and NQO1 and NQO2 activities with quinone-like drug metabolites. Hepatic NQO1 concentrations ranged from 8 to 213 nM. Using recombinant NQO1, we showed that low nM concentrations of NQO1 are sufficient to reduce synthetic amodiaquine and carbamazepine quinone-like metabolites in vitro. Hepatic NQO2 concentrations ranged from 2 to 31 μM. NQO2 catalyzed the reduction of quinone-like metabolites derived from acetaminophen, clozapine, 4′-hydroxydiclofenac, mefenamic acid, amodiaquine, and carbamazepine. The reduction of the clozapine nitrenium ion supports association studies showing that NQO2 is a genetic risk factor for clozapine-induced agranulocytosis. The 5-hydroxydiclofenac quinone imine, which was previously shown to be reduced by NQO1, was not reduced by NQO2. Tacrine was identified as a potent NQO2 inhibitor and was applied to further confirm the catalytic activity of NQO2 in these assays. While the in vivo relevance of NQO2-catalyzed reduction of quinone-like metabolites remains to be established by identification of the physiologically relevant co-substrates, our results suggest an additional protective role of the NQO2 protein by non-enzymatic scavenging of quinone-like metabolites. Hepatic NQO1 activity in detoxication of quinone-like metabolites becomes especially important when other detoxication pathways are exhausted and NQO1 levels are induced.

GSK3β is a key regulator of the ROS-dependent necrotic death induced by the quinone DMNQ

“…We show that GSK3β is responsible for reducing the antioxidant response engaged by NRF2. This response leads the up-regulation of the obligatory two-electron reducing flavoenzymes NQO1 and NQO2 47,48,51,52 . These flavoenzymes are required to blunt the redox cycling activity of DMNQ.…”

“…To demonstrate the key role of NQO1 and NQO2 in the necrotic response triggered by DMNQ, U87MG/GSK3β +/+ , GSK3β −/− or GSK3β −/− expressing GSK3β-GFP were treated with dicoumarol a potent inhibitor of NQO1 and tacrine, a recently identified NQO2 inhibitor 51,52 . The resistance to DMNQ-induced necrosis observed in the absence of GSK3β was completely abolished by the inhibition of NQO1, as well as, after the inhibition of NQO2, although less efficiently (Fig.…”

S29434, a Quinone Reductase 2 Inhibitor: Main Biochemical and Cellular Characterization

“…A screen of about 20,000 compounds from our library, comprising natural products such as flavonoids (Boutin et al, 2005), added further candidates to the list of QR2 inhibitors. Already on this list were resveratrol (Buryanovskyy et al, 2004), tacrine (den Braver-Sewradj et al, 2018), chloroquine (CLQ) (Kwiek et al, 2004), dabigatran (a prescription thrombin inhibitor) (Michaelis et al, 2012), and tetracyclic compounds (Boussard et al, 2006). Some products of quinone reduction are fairly unstable, especially in the absence of a conjugating system(s), so the reaction products (quinols) may spontaneously yield back the original quinones in the presence of oxygen.…”

The Biochemical Pathways of Nicotinamide-Derived Pyridones

“…Acetaminophen, also known as paracetamol is oxidized to a quinone by the FDXR-dependent cytochrome CYP450, CYP2E1, for which acetaminophen administration stimulates the overexpression [ 44 ]. acetaminophen exposure also promotes the overexpression of NADPH: quinone oxide-reductase 1 (NQO1) [ 45 ], an homolog of NQO2, which catalyzes the reduction of the quinone back to acetaminophen. Catabolites of vitamin B3 found in urine include nicotinuric acid, trigonelline, methyl-nicotinamide, Me-2PY, Me-4PY, and 4PYR.…”

“…NQO1 and NQO2 are FAD-dependent redox enzymes that bind NAD(P)H and NRH, respectively, and could potentially generate 4NAD(P)O and 4PYR via a mechanism like that of FDXR. Recent work on NQO2 and acetaminophen in the presence of NRH has identified superoxide HOO- as a by-product of the NQO2-catalyzed turn-over, especially in the presence of O 2 [ 45 ]. We envisage that the detection of 4PYR in the NQO2-catalyzed oxidation of NRH is promoted by the NQO2-catalyzed production of superoxide upon the reduction of NRH, with O 2 as a co-oxidant and that the production of superoxide within the vicinity of a still FAD-NQO2-bound NR, favors the addition of superoxide onto the electrophilic NR.…”