N-Demethylation Is a Major Route of 2-Amino-3-Methylimidazo[4,5-f]quinoline Metabolism in Mouse

Abstract

2-Amino-3-methylimidazo[4,5-f]quinoline (IQ) is a heterocyclic amine (HCA) formed by high-temperature cooking of proteinaceous food (Felton and Knize, 1990). More than 20 similarly formed HCAs have been identified. In the human diet, consumption of 400 g of cooked lean meat could result in exposure to several micrograms of mutagenic HCAs. These amines are detected in urine and their excretion, as unchanged amine, is increased by a cytochrome P450 (P450) inhibitor (Lynch et al., 1992;Boobis et al., 1994), indicating their absorption from cooked foods and P450 metabolism.IQ is a potent carcinogen inducing tumors in multiple tissues and in different species (National Toxicology Program Report on Carcinogens: Background Document for Heterocyclic Amines: MeIQ, MeIQx, IQ, and PhIP, 2005, http://ntp.niehs.nih.gov/ntp/roc/eleventh/ profiles/s092vhca.pdf). In mouse, oral administration of IQ caused forestomach, liver, and lung tumors in both sexes. Although IQ also caused tumors in several organs in both sexes of rats, mammary and clitoral gland tumors were only detected in females and colon and skin tumors only in males. IQ administered orally to monkeys or mice caused liver tumors. Using a colitis-induced carcinogenicity model with ApcMin/ϩ mice (Cooper et al., 2001), we have preliminary data indicating that induction of colitis by treatment with 4% dextran sulfate sodium (DSS) in drinking water followed by oral doses of 40 mg/kg IQ resulted in a 100% incidence of invasive colorectal tumors, whereas mice treated with only DSS had no tumors (Clapper et al., 2006). The strong association of intake of high-temperature cooked meat and colorectal cancer risk (Giovannucci et al., 1994), the presence of HCAs in cooked meat (Felton and Knize, 1990), and the initiation of colon cancer by HCAs (Kristiansen et al., 1997) suggest that HCAs present in high-temperature cooked meat may be responsible for the increased risk of colon cancer associated with this dietary component.Activation of IQ is thought to involve N-oxidation by P450, followed by O-acetylation with subsequent formation of a reactive intermediate, nitrenium ion, that binds DNA (Turesky et al., 1991). These DNA adducts are thought to cause mutations that initiate carcinogenesis. After IQ administration, DNA adducts are found in a variety of rodent and nonhuman primate tissues (Nerurkar et al., 1995;Turesky et al., 1996). Whereas N-oxidation of IQ has been demonstrated with rat microsomes (Turesky et al., 1998), excretion of

Identification of New 2-Amino-3-methylimidazo[4,5-f]quinoline Urinary Metabolites from β-Naphthoflavone-Treated Mice

“…Three new metabolites of m/z 233, 393, and 217 were also observed by ESI/MS in the positive-ion mode (data not shown). The metabolite of m/z 217 was also present in control mice but not previously reported (Lakshmi et al, 2008). In control mice, the relative abundance of excreted metabolites was 5-O-glucuronide Ͼ demethyl-IQ Ͼ sulfamate Ͼ N-glucuronide Ͼ m/z 217 Ͼ 5-sulfate, similar to previously reported (Lakshmi et al, 2008).…”

“…Metabolites were identified by their HPLC elution time relative to authentic rat products previously identified by us (Armbrecht et al, 2007;Lakshmi et al, 2008) and susceptibility to specific treatments Snyderwine et al, 1992). Urinary metabolites were purified before assessing their susceptibility.…”

“…Mouse IQ urinary metabolites identified earlier were purified using HPLC solvent systems described previously (Lakshmi et al, 2008). Purification of the new early eluting metabolites uses the following HPLC solvent systems at a flow rate of 1 ml/min: solvent system 2, the mobile phase contained 20 mM ammonium formate, pH 3.1, in 0% acetonitrile from 0 to 10 min, 0 to 40% acetonitrile from 10 to 15 min, and 40 to 0% acetonitrile from 20 to 25 min; solvent system 3, the mobile phase contained 20 mM ammonium acetate, pH 7.8, in 0% methanol from 0 to 2 min, 0 to 2% methanol from 2 to 7 min, 2 to 3.2% from 10 to 17 min, 3.2 to 35% methanol from 27 to 32 min, and 35 to 0% from 35 to 40 min; solvent 4, the mobile phase contained 0.1% glacial acetic acid, pH 3.0, in 0% methanol from 0 to 2 min, 0 to 2.5% methanol from 2 to 7 min, 2.5 to 50% methanol from 10 to 15 min, and 50 to 0% methanol from 15 to 20 min; solvent 5, the mobile phase contained 20 mM ammonium acetate, pH 7.8, in 0% methanol from 0 to 15 min, 0 to 0.15% methanol from 15 to 30 min, 0.15 to 40% methanol from 30 to 35 min, and 40 to 0% methanol from 40 to 45 min; solvent 6, the mobile dmd.aspetjournals.org phase contained 20 mM ammonium acetate, pH 7.8, in 0% acetonitrile from 0 to 15 min, 0 to 0.15% acetonitrile from 15 to 30 min, 0.15 to 40% acetonitrile from 30 to 35 min, and 40 to 0% acetonitrile from 40 to 45 min; and solvent 7, the mobile phase contained 0.1% glacial acetic acid, pH 3.0, in 0% acetonitrile from 0 to 15 min, 0 to 40% acetonitrile from 15 to 20 min, and 40 to 0% acetonitrile from 25 to 30 min.…”

“…For example, several studies in humans have detected HCA metabolites, which are not present in rats and have not yet been identified (Turesky et al, 1998;Garner et al, 1999;Langouët et al, 2001). In addition, N-demethylation is a primary pathway for HCA in humans (Langouët et al, 2001) and monkeys (Snyderwine et al, 1992) but is not detected in rats (Armbrecht et al, 2007;Lakshmi et al, 2008). 2-Amino-imidazo[4,5-f]quinoline (demethyl-IQ) is mutagenic (Barnes et al, 1985).…”

The Effect of Flavonoids in Soybean Products in Lymphocytes from IBD and Colon Cancer Patients After Treatment with Food Mutagens and Hydrogen Peroxide

“…Hence, PhIP may induce/enhance carcinogenicity via DNA damage and/or oestrogen receptors (Bennion et al, 2005;Felton et al, 2004). IQ on the other hand can form DNA adducts like N- (Lakshmi et al, 2008). In our study the DNA damage induced in lymphocytes of both donor groups by food mutagens IQ and PhIP was effectively and dose-dependently reduced by supplementation with the flavonoids quercetin and rutin (Table 3).…”