Disease relevance of CCRIS 4107

• This divergent behavior of PhIP and N-hydroxy-PhIP in Salmonella may also be a key to the understanding of several 'unusual' properties of PhIP in mammalian cells and organisms [1].

High impact information on CCRIS 4107

• The presence of the glucuronide conjugate of N-hydroxy-PhIP in the urine of pups and the lack of detectable conjugate or N-hydroxylamine itself in breast milk suggest that PhIP from breast milk undergoes metabolic activation via N-hydroxylation in 5-day-old rat pups [2].
• The current study examines the expression and catalytic activity of NAT toward the N-hydroxy-HCAs 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-hydroxy-PhIP) and 2-hydroxy-amino-3-methylimidazo[4,5-f]quinoline (N-hydroxy-IQ) in the human mammary gland [3].
• The formation of DNA adducts and metabolites from colon slices exposed to N-hydroxy-PhIP but not PhIP implies that there is insufficient P450 activity in the rat colon to activate PhIP to hydroxylated metabolites, suggesting that the rat colon is a site of Phase II metabolism for PhIP and that the liver is the primary source for hydroxylation [4].
• In addition, liver microsomes, unlike intestinal microsomes, were able to convert PhIP to the proximate mutagen N-hydroxy-PhIP [5].
• These results indicate that UGT1A-mediated glucuronidation of PhIP and N-hydroxy-PhIP is an important pathway for PhIP detoxification, and demonstrate the importance of tissue-specific metabolism [6].

Biological context of CCRIS 4107

• Only N-hydroxy-PhIP (at 10 and 50 microM), however, was cytotoxic as assessed by the MTT cell survival assay (which measures the capacity of mitochondria to metabolize a tetrazolium salt) [7].
• The plasmids were treated in vitro with 0, 5, 10, or 40 microM N-hydroxy-IQ or N-hydroxy-PhIP in the presence of a 10-fold molar excess of acetic anhydride to generate the N-acetoxy derivatives in situ [8].
• To examine if PhIP and its reactive metabolite N-hydroxy-PhIP inhibit apoptosis in human mammary epithelial MCF-10A cells, confluent cultures deprived of serum and growth factors were incubated for 24 h with either compound [9].
• Following N-hydroxylation, N-acetyltransferases catalyze the O-acetylation (activation) of N-hydroxy-PhIP to an electrophile causing DNA damage [10].
• N-hydroxy-PhIP O-sulfotransferase activities did not vary with acetylator genotype [11].

Anatomical context of CCRIS 4107

• This metabolite, which also was formed in incubations with either 4'-hydroxy-PhIP or N-hydroxy-PhIP, was produced by microsomes from uninduced animals at a much slower rate [12].
• When isolated rat mammary epithelial cells (from untreated rats) were incubated in vitro with N-hydroxy-PhIP (45 microM, 1 h, 37 degrees C), PhIP-DNA adducts were detected in cell DNA (RAL = approximately 97 x 10(7); however, no adducts were detected in cells incubated with PhIP (200 microM, 15 h, 37 degrees C) [13].
• In contrast, no significant adenosine 3'-phosphate 5'-phosphosulfate-dependent activation of N-hydroxy-IQ was observed with monkey cytosol from liver, kidney, heart or colon but the sulfotransferase-mediated activation of N-hydroxy-PhIP was at least 10 times higher in all four tissues of monkeys than in rats [14].
• In contrast, N-hydroxy-PhIP was metabolically activated by cytosol-catalyzed PhIP-DNA adduct formation to calf thymus DNA incubated in vitro with N-hydroxy-PhIP (2 microM) in the presence of acetyl CoA [13].
• The presence of the glucuronide conjugate of N-hydroxy-PhIP in urine, bile and plasma, and the presence of PhIP-DNA adducts in white blood cells indicate that PhIP undergoes metabolic activation via N-hydroxylation in cynomolgus monkeys [15].

Associations of CCRIS 4107 with other chemical compounds

• Incubating cells with pentachlorophenol, an inhibitor of acetyltransferase, or incubating cells at 0-4 degrees C, reduced N-hydroxy-PhIP adduct levels by 45 and 75% respectively, indicating that formation of N-hydroxy-PhIP adducts was largely due to metabolic activation [13].
• Isolated cardiomyocytes treated with 1.2 mM N-acetylcysteine before and during exposure to N-hydroxy-IQ or N-hydroxy-PhIP showed a smaller percentage of ultrastructural abnormalities, such as myofilament loss, sarcoplasmic reticulum swelling and abnormal mitochondria [16].
• Resveratrol modulates human mammary epithelial cell O-acetyltransferase, sulfotransferase, and kinase activation of the heterocyclic amine carcinogen N-hydroxy-PhIP [17].

Gene context of CCRIS 4107

• These results clearly show that UGT1A1 has the highest specificity for glucuronidating N-hydroxy-PhIP [18].
• In contrast, N-hydroxy-PhIP was activated specifically by human SULT1A1, but not by NAT1 or NAT2 [19].
• All UGT1A proteins except UGT1A6 showed some degree of activity toward N-hydroxy-PhIP [18].
• Large differences in the metabolic activation via O-acetylation of 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-hydroxy-PhIP) were noted for NAT1 allelic variants [20].
• The prostate has potential for GSTP1-dependent detoxification of ATP-activated N-hydroxy-PhIP but little potential for detoxification of N-acetoxy-PhIP by GSTA1 [21].

Analytical, diagnostic and therapeutic context of CCRIS 4107

• To determine which UGT isozymes are involved in the biotransformation of PhIP and the cytochrome P4501A2-mediated reactive intermediate N-hydroxy-PhIP, microsomes expressing human UGT1A1, -1A4, -1A6 or -1A9 were incubated with PhIP and N-hydroxy-PhIP and the reaction products analyzed by HPLC and ESI-MS [22].

References