Hemin potentiates nitric oxide-mediated nitrosation of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) to 2-nitrosoamino-3-methylimidazo[4,5-f]quinoline.
Heme has been reported to be an important contributor to endogenous N-nitrosation within the colon and to the enhanced incidence of colon cancer observed with increased intake of red meat. This study uses the heterocyclic amine 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) as a target to evaluate hemin potentiation of nitric oxide (NO)-mediated nitrosation. Formation of 14C-2-nitrosoamino-3-methylimidazo[4,5-f]quinoline (N-NO-IQ) was monitored by HPLC following incubation of 10 microM IQ with the NO donor spermine NONOate (1.2 microM NO/min) at pH 7.4 in the presence or absence of hemin. N-NO-IQ formation due to autoxidation of NO was at the limit of detection (0.1 microM) and increased 22-fold in the presence of 10 microM hemin and an in situ system for generating H2O2 (glucose oxidase/glucose). A linear increase in N-NO-IQ formation was observed from 1 to 10 microM hemin. Significant nitrosamine formation occurred at fluxes of NO and H2O2 as low as 0.024 and 0.25 microM/min, respectively. Potentiation by hemin was not affected by a 400-fold excess flux of H2O2 over NO or a 4.8-fold excess flux of NO over H2O2. Reactive nitrogen species produced by hemin potentiation had a 46-fold greater affinity for IQ than those produced by autoxidation. Azide inhibited autoxidation, suggesting involvement of the nitrosonium ion, NO+. Hemin potentiation was inhibited by NADH, but not azide, suggesting oxidative nitrosylation with NO2* or a NO2*-like species. IQ and 2,3-diaminonaphthylene were much better targets for nitrosation than the secondary amine morpholine. Apc(min) mice with dextran sulfate sodium-induced colitis demonstrated increased levels of urinary nitrite and nitrate consistent with increased expression of iNOS and NO synthesis. As reported previously, identical conditions increased fecal N-nitroso compounds. Thus, hemin potentiation of NO-mediated nitrosation of heterocyclic amines provides a testable mechanism by which red meat consumption can generate N-nitroso compounds and initiate colon cancer under inflammatory conditions, such as colitis.
Lakshmi
Vijaya M
VM
VA Medical Center, Division of Geriatric Medicine and Department of Biochemistry and Molecular Biology, St. Louis University School of Medicine, St. Louis, Missouri 63125, USA.
Clapper
Margie L
ML
Chang
Wen-Chi
WC
Zenser
Terry V
TV
D000818:Animals; D002273:Carcinogens / Q000737:chemistry / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D016264:Dextran Sulfate / Q000493:pharmacokinetics; D005260:Female; D006427:Hemin / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D008817:Mice, Mutant Strains; D009569:Nitric Oxide / Q000737:chemistry / Q000378:metabolism*; D015538:Nitrosation; D011804:Quinolines / Q000737:chemistry / Q000378:metabolism*; D026361:Reactive Nitrogen Species / Q000737:chemistry / Q000378:metabolism
D002273:Carcinogens; D011804:Quinolines; D026361:Reactive Nitrogen Species; C055822:2-azido-3-methylimidzo(4,5-f)quinoline; C029216:2-amino-3-methylimidazo(4,5-f)quinoline; D009569:Nitric Oxide; D006427:Hemin; D016264:Dextran Sulfate