Linked Life Data

7614688

Source:http://linkedlifedata.com/resource/pubmed/id/7614688

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
7
pubmed:dateCreated
1995-8-24
pubmed:abstractText
The promutagenic and procarcinogenic heterocyclic amines (HAs) found in cooked meats are N-hydroxylated by microsomal cytochrome P450 enzymes as the first step in their metabolic activation. In cynomolgus monkeys, one of the HAs, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), has been shown to be a potent hepatocarcinogen. However, the structurally similar HA 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) lacks this potency to induce hepatocellular carcinoma in monkeys. Liver microsomes from cynomolgus monkeys show a striking substrate specificity for the metabolic activation of IQ and MeIQx, the former being a far better substrate for N-hydroxylation. Western blot analysis showed that cynomolgus monkey hepatic microsomes constitutively express P450s immunologically related to the human CYP3A, CYP2C, and low levels of CYP1A1. For comparison, Western blot analysis of rat, human and patas monkey microsomes was also carried out. Treatment of cynomolgus monkeys with rifampicin induced hepatic cytochromes P450 related to human CYP3A4 and CYP2C9/10 without inducing CYP1A1 or CYP1A2. Immunoblot analysis also showed that chronic exposure of cynomolgus monkeys to IQ induced hepatic microsomal cytochrome CYP1A1 and CYP1A2, similarly but lesser in magnitude to that observed with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCCD) induction. Using the Ames Salmonella mutagenicity assay, we examined the effect of the inducers on the mutagenic activation (i.e. N-hydroxylation) of IQ and MeIQx by cynomolgus monkey hepatic microsomes. We also examined the mutagenic activation of these HAs by rat, human and patas monkey liver microsomes. Microsomes from cynomolgus monkeys treated with rifampicin showed a 3-fold increase in the mutagenic activation of IQ but showed no increase in the mutagenic activation of MeIQx. Since cytochromes P4503A and/or P4502C are constitutively expressed in cynomolgus monkey hepatic microsomes, and upon induction with rifampicin are associated with an increased metabolic activation of IQ but not MeIQx, it appears that CYP3A and/or CYP2C are the isoform(s) showing the selective substrate specificity in the metabolic activation of IQ over MeIQx. Treatment of monkeys with TCDD significantly increased the mutagenic activation of both IQ and MeIQx, concomitant with an induction of CYP1A isozymes. Thus, it appears that TCDD-inducible CYP1A enzymes N-hydroxylate both substrates without selectivity. Together, these findings suggest that CYP3A and CYP2C are the principal isoforms in the cynomolgus monkey, associated with the metabolic activation implicated in the induction of hepatocarcinogenicity by IQ. Furthermore, the poor metabolic activation of MeIQx by CYP3A and CYP2C, coupled with low constitutive levels of CYP1A isozymes, provide a metabolic explanation for the low hepatocarcinogenic potency of MeIQx in cynomolgus monkeys.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Jul
pubmed:issn
0143-3334
pubmed:author
pubmed:issnType
Print
pubmed:volume
16
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
1549-55
pubmed:dateRevised
2006-11-15
pubmed:meshHeading
pubmed-meshheading:7614688-Animals, pubmed-meshheading:7614688-Biotransformation, pubmed-meshheading:7614688-Cytochrome P-450 Enzyme System, pubmed-meshheading:7614688-Enzyme Induction, pubmed-meshheading:7614688-Erythrocebus patas, pubmed-meshheading:7614688-Female, pubmed-meshheading:7614688-Humans, pubmed-meshheading:7614688-Hydroxylation, pubmed-meshheading:7614688-Immunoblotting, pubmed-meshheading:7614688-Isoenzymes, pubmed-meshheading:7614688-Macaca fascicularis, pubmed-meshheading:7614688-Male, pubmed-meshheading:7614688-Microsomes, Liver, pubmed-meshheading:7614688-Mutagenicity Tests, pubmed-meshheading:7614688-Mutagens, pubmed-meshheading:7614688-Quinolines, pubmed-meshheading:7614688-Quinoxalines, pubmed-meshheading:7614688-Rats, pubmed-meshheading:7614688-Rifampin, pubmed-meshheading:7614688-Species Specificity, pubmed-meshheading:7614688-Substrate Specificity, pubmed-meshheading:7614688-Tetrachlorodibenzodioxin
pubmed:year
1995
pubmed:articleTitle
Cytochromes P450 in cynomolgus monkeys mutagenically activate 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) but not 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx).
pubmed:affiliation
Laboratory of Experimental Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4255, USA.
pubmed:publicationType
Journal Article, Comparative Study