Cancer Res. 1988 Aug 15;48(16):4513-9.  

Specificity of rabbit cytochrome P-450 isozymes involved in the metabolic
activation of the food derived mutagen 2-amino-3-methylimidazo[4,5-f] quinoline.

McManus ME, Burgess W, Snyderwine E, Stupans I.

Department of Clinical Pharmacology, School of Medicine, Flinders University of
South Australia, Bedford Park.

The involvement of rabbit liver cytochromes P-450 in the activation of the food
derived heterocyclic amine mutagen, 2-amino-3-methylimidazo[4,5-f]quinoline
(IQ), was assessed using the Ames/Salmonella test. The number of revertants
induced by IQ per microgram of control rabbit liver microsomes was 1872 +/- 50
(SD, n = 3), and this increased to 3690 +/- 239 when microsomes from
2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) animals were used as the metabolic
activation source. Microsomes from phenobarbital, rifampicin, and acetone
pretreated rabbits were less efficient the controls at activating IQ to a
mutagen. Cytochrome P-450 Forms 4 and 6, which are induced by TCDD, were found
to be efficient activators of IQ to a mutagen in reconstitution experiments.
Form 4 was 7.7-fold more active than Form 6 and produced 1702 revertants/0.125
pmol with a 20-min preincubation step in the Ames test. Anti-Form 4 IgG
inhibited the activation of IQ in control and TCDD induced microsomes by 78 and
79%, respectively. The contents of cytochrome P-450 Form 4, determined by
Western blot analysis, in control and phenobarbital, acetone, rifampicin, and
TCDD pretreated microsomes were 0.55 +/- 0.19, 0.63 +/- 0.34, 0.5 +/- 0.27, 0.28
+/- 0.16, and 2.19 +/- 0.43 (n = 3) nmol/mg protein, respectively. A highly
significant statistical correlation existed between the capacity of the above
microsomes to activate IQ to a mutagen and their cytochrome P-450 Form 4 content
(r = 0.96; r2 = 0.92). The content of cytochrome P-450 Form 6 in the above
microsomes was also highly correlated with their capacity to activate IQ (r =
0.92; r2 = 0.85). Based on these results and the tissue distribution of
cytochrome P-450 Forms 4 and 6, the former obviously contributes most toward the
activation of IQ in the liver, whereas Form 6 would be expected to be primarily
involved in this process in extrahepatic tissues.

PMID: 3396004 [PubMed - indexed for MEDLINE]