Bioactivation versus Detoxication of the Urothelial Carcinogen Aristolochic Acid I by Human Cytochrome P450 1A1 and 1A2

Abstract

Exposure to aristolochic acid (AA) is associated with human nephropathy and urothelial cancer. Individual susceptibility to AA-induced disease likely reflects individual differences in enzymes that metabolize AA. Herein, we evaluated AAI metabolism by human cytochrome P450 (CYP) 1A1 and 1A2 in two CYP1A-humanized mouse lines that carry functional human CYP1A1 and CYP1A2 genes in the absence of the mouse Cyp1a1/1a2 orthologs. Human and mouse hepatic microsomes and human CYPs were also studied. Human CYP1A1 and 1A2 were found to be principally responsible for reductive activation of AAI to form AAI-DNA adducts and for oxidative detoxication to 8-hydroxyaristolochic acid (AAIa), both in the intact mouse and in microsomes. Overall, AAI-DNA adduct levels were higher in CYP1A-humanized mice relative to wild-type mice, indicating that expression of human CYP1A1 and 1A2 in mice leads to higher AAI bioactivation than in mice containing the mouse CYP1A1 and 1A2 orthologs. Furthermore, an exclusive role of human CYP1A1 and 1A2 in AAI oxidation to AAIa was observed in human liver microsomes under the aerobic (i.e., oxidative) conditions. Because CYP1A2 levels in human liver are at least 100-fold greater than those of CYP1A1 and there exists a > 60-fold genetic variation in CYP1A2 levels in human populations, the role of CYP1A2 in AAI metabolism is clinically relevant. The results suggest that, in addition to CYP1A1 and 1A2 expression levels, in vivo oxygen concentration in specific tissues might affect the balance between AAI nitroreduction and demethylation, which in turn would influence tissue-specific toxicity or carcinogenicity.

Impact of genetic modulation of SULT1A enzymes on DNA adduct formation by aristolochic acids and 3-nitrobenzanthrone

“…Groups male mice ( n  = 4; 8–10 weeks of age) were used throughout the study. WT, hSULT1A1/2 , Sult1a1(−/−) and Sult1d1(−/−) mice were treated with a single dose of 50 mg/kg body weight AAI or AAII by oral gavage according to treatment protocols used previously to study AA metabolism (Arlt et al 2011; Levova et al 2011; Stiborova et al 2012). AAI and AAII (as sodium salts) were dissolved in water at a concentration of 5 mg/mL.…”

“…1a) (Stiborova et al 2013, 2014a). Several human enzymes capable of activating AA by nitroreduction have been identified and include cytosolic NAD(P)H:quinone oxidoreductase (NQO1) (Stiborova et al 2002, 2003), and microsomal enzymes including cytochrome P450 (CYP) 1A1, CYP1A2 and NADPH:CYP oxidoreductase (Arlt et al 2011, 2015a; Stiborova et al 2001a, 2005, 2012). It has been shown that both AAI and AAII exert their genotoxic and carcinogenic properties by DNA adduct formation and that reductive metabolic activation is a prerequisite for generation of DNA adducts in vivo and in vitro (Gokmen et al 2013; Schmeiser et al 2009).…”

“…It is well known that conjugation reactions catalysed by phase II enzymes are often involved in the activating metabolism of carcinogenic nitroaromatics (Arlt et al 2005; Glatt and Meinl 2004; Glatt et al 2016; Rendic and Guengerich 2012). Phase II metabolites of AA have been found in the urine and faeces of AA-treated rodents and include the N - and O -glucuronide of aristolactam Ia and the O 8 -glucuronide, the O 8 -acetate and O 8 -sulfonated ester of AAIa (Chan et al 2007); AAIa is considered to be a detoxification product (Levova et al 2011; Stiborova et al 2012). As shown for other aromatic hydroxylamines (Glatt and Meinl 2004; Glatt et al 2016), like those generated during the metabolism of 3-nitrobenzanthrone (3-NBA) (Arlt et al 2002b, 2003, 2005), the N -hydroxyaristolactams may be further activated by O -acetylation or O -sulfonation to reactive esters capable of generating the same electrophilic species (aristolactam-nitrenium ions) as formed by direct cleavage of the hydroxyl group.…”

Aristolochic acid I is a substrate of BCRP but not P-glycoprotein or MRP2

“…The toxic mechanism of AAI, especially the P450-mediated AAI metabolic activation, has been extensively investigated (Chan et al, 2007;Levova et al, 2011;Stiborova et al, 2012). The metabolism profile of AAI was clearly reported (Stiborova et al, 2013).…”

Aristolochic Acid-Induced Nephrotoxicity: Molecular Mechanisms and Potential Protective Approaches

“…Studies on the metabolism of AA have reported the involvement of several enzymes that catalyze the reduction reactions resulting in bioactivation of AA [25,29]. The most important of these enzymes include cytosolic nicotinamide adenine dinucleotide phosphate (NADPH):quinone oxidoreductase 1 (NQO1), microsomal cytochrome P450 (CYP) mainly 1A1, CYP1A2, renal microsome NADPH:CYP oxidoreductase (POR), and prostaglandin H synthase [25,30,31].…”