Assessment of the DNA adduction and pharmacokinetics of PhIP and MeIOx in rodents at doses approximating human exposure using the technique of accelerator mass spectrometry (AMS) and 32P-postlabeling.

Ken W Turteltaub, J. S. Vogel, C. Frantz, J. S. Felton, M. McManus

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Abstract

Estimating the cancer risk posed by heterocyclic amines depends on measuring how chemical dose influences measurable indicators of cancer progression. This data ideally should encompass the range of actual human exposure, at the low dose end, and laboratory animal studies, at the high dose end. Accelerator mass spectrometry (AMS) has been used to measure the absorption, fate, and DNA adduct dosimetry of the heterocyclic amines PhIP and MeIQx at doses equivalent to human consumption following single-dose administration and chronic daily dosing. AMS is a nuclear physics technique which specifically counts nuclei of cosmogenic isotopes, rather than relying on decay. For tracing 14C, sensitivity is increased 10(6)-fold relative to decay counting. We have found that tissue clearance rates for [2-(14)C]-PhIP are rapid (t1/2 = 1 h) at low dose (41 ng/kg), with most of the radiocarbon distributed to the liver and G.I. tract. MeIQx-DNA adduct levels decrease linearly with dose (5 mg/kg-500 ng/kg) in single dose exposures. Likewise, the biologically available dose of [2-(14)C]-MeIQx decreases linearly with decreasing dose (5 mg/kg-1 ng/kg). On chronic daily dosing, it takes 40 days for adducts to reach steady-state in tissues and adduct levels appear to decrease linearly with decreasing dose, except possibly at very low doses. DNA binding of PhIP involves both sulfation or acetylation of the N-hydroxylated PhIP. Quantitatively, sulfation appears to be an important pathway for PhIp activation in rodent tissue cytosols while acetylation appears quantitatively more important in human tissue cytosols. The greatest activity is in liver and intestinal tissues for both pathways. The specific DNA adducts formed in vivo and in vitro from exposure to PhIP and MeIQx are likely guanine adducts. These data suggest that DNA adduct dosimetry responds linearly with dose but may become sub-linear at very low doses for chronic exposure and that factors other than DNA adduction may be critical to explain these heterocyclic amines' tumorigenicity.

Original languageEnglish (US)
Pages (from-to)93-102
Number of pages10
JournalPrincess Takamatsu symposia
Volume23
StatePublished - 1995
Externally publishedYes

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DNA Adducts
Rodentia
Mass Spectrometry
Pharmacokinetics
DNA
Amines
Acetylation
Cytosol
Nuclear Physics
Liver
Guanine
Laboratory Animals
Isotopes
Gastrointestinal Tract
Neoplasms
2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine

Cite this

@article{b240f1a5448f4dc8b15494f7d969b5b0,
title = "Assessment of the DNA adduction and pharmacokinetics of PhIP and MeIOx in rodents at doses approximating human exposure using the technique of accelerator mass spectrometry (AMS) and 32P-postlabeling.",
abstract = "Estimating the cancer risk posed by heterocyclic amines depends on measuring how chemical dose influences measurable indicators of cancer progression. This data ideally should encompass the range of actual human exposure, at the low dose end, and laboratory animal studies, at the high dose end. Accelerator mass spectrometry (AMS) has been used to measure the absorption, fate, and DNA adduct dosimetry of the heterocyclic amines PhIP and MeIQx at doses equivalent to human consumption following single-dose administration and chronic daily dosing. AMS is a nuclear physics technique which specifically counts nuclei of cosmogenic isotopes, rather than relying on decay. For tracing 14C, sensitivity is increased 10(6)-fold relative to decay counting. We have found that tissue clearance rates for [2-(14)C]-PhIP are rapid (t1/2 = 1 h) at low dose (41 ng/kg), with most of the radiocarbon distributed to the liver and G.I. tract. MeIQx-DNA adduct levels decrease linearly with dose (5 mg/kg-500 ng/kg) in single dose exposures. Likewise, the biologically available dose of [2-(14)C]-MeIQx decreases linearly with decreasing dose (5 mg/kg-1 ng/kg). On chronic daily dosing, it takes 40 days for adducts to reach steady-state in tissues and adduct levels appear to decrease linearly with decreasing dose, except possibly at very low doses. DNA binding of PhIP involves both sulfation or acetylation of the N-hydroxylated PhIP. Quantitatively, sulfation appears to be an important pathway for PhIp activation in rodent tissue cytosols while acetylation appears quantitatively more important in human tissue cytosols. The greatest activity is in liver and intestinal tissues for both pathways. The specific DNA adducts formed in vivo and in vitro from exposure to PhIP and MeIQx are likely guanine adducts. These data suggest that DNA adduct dosimetry responds linearly with dose but may become sub-linear at very low doses for chronic exposure and that factors other than DNA adduction may be critical to explain these heterocyclic amines' tumorigenicity.",
author = "Turteltaub, {Ken W} and Vogel, {J. S.} and C. Frantz and Felton, {J. S.} and M. McManus",
year = "1995",
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journal = "Princess Takamatsu symposia",

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T1 - Assessment of the DNA adduction and pharmacokinetics of PhIP and MeIOx in rodents at doses approximating human exposure using the technique of accelerator mass spectrometry (AMS) and 32P-postlabeling.

AU - Turteltaub, Ken W

AU - Vogel, J. S.

AU - Frantz, C.

AU - Felton, J. S.

AU - McManus, M.

PY - 1995

Y1 - 1995

N2 - Estimating the cancer risk posed by heterocyclic amines depends on measuring how chemical dose influences measurable indicators of cancer progression. This data ideally should encompass the range of actual human exposure, at the low dose end, and laboratory animal studies, at the high dose end. Accelerator mass spectrometry (AMS) has been used to measure the absorption, fate, and DNA adduct dosimetry of the heterocyclic amines PhIP and MeIQx at doses equivalent to human consumption following single-dose administration and chronic daily dosing. AMS is a nuclear physics technique which specifically counts nuclei of cosmogenic isotopes, rather than relying on decay. For tracing 14C, sensitivity is increased 10(6)-fold relative to decay counting. We have found that tissue clearance rates for [2-(14)C]-PhIP are rapid (t1/2 = 1 h) at low dose (41 ng/kg), with most of the radiocarbon distributed to the liver and G.I. tract. MeIQx-DNA adduct levels decrease linearly with dose (5 mg/kg-500 ng/kg) in single dose exposures. Likewise, the biologically available dose of [2-(14)C]-MeIQx decreases linearly with decreasing dose (5 mg/kg-1 ng/kg). On chronic daily dosing, it takes 40 days for adducts to reach steady-state in tissues and adduct levels appear to decrease linearly with decreasing dose, except possibly at very low doses. DNA binding of PhIP involves both sulfation or acetylation of the N-hydroxylated PhIP. Quantitatively, sulfation appears to be an important pathway for PhIp activation in rodent tissue cytosols while acetylation appears quantitatively more important in human tissue cytosols. The greatest activity is in liver and intestinal tissues for both pathways. The specific DNA adducts formed in vivo and in vitro from exposure to PhIP and MeIQx are likely guanine adducts. These data suggest that DNA adduct dosimetry responds linearly with dose but may become sub-linear at very low doses for chronic exposure and that factors other than DNA adduction may be critical to explain these heterocyclic amines' tumorigenicity.

AB - Estimating the cancer risk posed by heterocyclic amines depends on measuring how chemical dose influences measurable indicators of cancer progression. This data ideally should encompass the range of actual human exposure, at the low dose end, and laboratory animal studies, at the high dose end. Accelerator mass spectrometry (AMS) has been used to measure the absorption, fate, and DNA adduct dosimetry of the heterocyclic amines PhIP and MeIQx at doses equivalent to human consumption following single-dose administration and chronic daily dosing. AMS is a nuclear physics technique which specifically counts nuclei of cosmogenic isotopes, rather than relying on decay. For tracing 14C, sensitivity is increased 10(6)-fold relative to decay counting. We have found that tissue clearance rates for [2-(14)C]-PhIP are rapid (t1/2 = 1 h) at low dose (41 ng/kg), with most of the radiocarbon distributed to the liver and G.I. tract. MeIQx-DNA adduct levels decrease linearly with dose (5 mg/kg-500 ng/kg) in single dose exposures. Likewise, the biologically available dose of [2-(14)C]-MeIQx decreases linearly with decreasing dose (5 mg/kg-1 ng/kg). On chronic daily dosing, it takes 40 days for adducts to reach steady-state in tissues and adduct levels appear to decrease linearly with decreasing dose, except possibly at very low doses. DNA binding of PhIP involves both sulfation or acetylation of the N-hydroxylated PhIP. Quantitatively, sulfation appears to be an important pathway for PhIp activation in rodent tissue cytosols while acetylation appears quantitatively more important in human tissue cytosols. The greatest activity is in liver and intestinal tissues for both pathways. The specific DNA adducts formed in vivo and in vitro from exposure to PhIP and MeIQx are likely guanine adducts. These data suggest that DNA adduct dosimetry responds linearly with dose but may become sub-linear at very low doses for chronic exposure and that factors other than DNA adduction may be critical to explain these heterocyclic amines' tumorigenicity.

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