Differences in caffeine 3-demethylation activity among inbred mouse strains: a comparison of hepatic Cyp1a2 gene expression between two inbred strains.
The 3-demethylation of caffeine can be used as an index of cytochrome P450 CYP1A2 activity in vivo. We compared the plasma levels of caffeine and the 3-demethylated metabolite. 1,7-dimethylxanthine, in six common inbred strains (A/J, P/J, BALB/cJ, C3H/HeJ, AKR/J, and SWR/J) and one inbred strain (APN) derived in our laboratory from outbred Swiss-Webster mice on the basis of its relative susceptibility to acetaminophen-induced hepatotoxicity. We found significant variations between a number of the common strains, all of which produced significantly higher caffeine 3-demethylation indices than our APN strain. In three of the six common strains, there was a significant difference between males and females, with the females having consistently lower 1,7-xanthine/caffeine ratios. Hepatic Cyp1a2 expression was compared between APN and C3H/HeJ males. Microsomal methoxyresorufin O-demethylation, acetanilide 4-hydroxylation, and CYP1A2 immunoreactive protein levels were significantly higher in C3H/HeJ relative to APN mice, as were hepatic CYP1A2 mRNA levels. These results indicate the importance of strain and gender to the outcome of pharmacological or toxicological studies involving CYP1A2-mediated metabolism, as well as the suitability of the plasma 1,7-dimethylxanthine/caffeine ratio as a marker of CYP1A2 activity in the mouse. The striking differences observed between the APN and C3H/HeJ mice suggest that these strains may be suitable for a genetic analysis of the regulation of the basal expression of CYP1A2, a key enzyme in procarcinogen activation.
Casley
W L
WL
Therapeutic Products Directorate, Health Canada, Banting Research Center, Ottawa, Ontario, Canada. bcasley@hpb.hwc.ca
Menzies
J A
JA
Girard
M
M
Larocque
L
L
Mousseau
N
N
Whitehouse
L W
LW
Moon
T W
TW
D000082:Acetaminophen / Q000008:administration & dosage; D000818:Animals; D002110:Caffeine / Q000008:administration & dosage* / Q000097:blood; D019363:Cytochrome P-450 CYP1A1 / Q000096:biosynthesis / Q000235:genetics; D019388:Cytochrome P-450 CYP1A2 / Q000096:biosynthesis* / Q000235:genetics; D018076:DNA, Complementary / Q000096:biosynthesis; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D015151:Immunoblotting; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D008862:Microsomes, Liver / Q000187:drug effects* / Q000201:enzymology; D015345:Oligonucleotide Probes; D010641:Phenotype; D012333:RNA, Messenger / Q000032:analysis; D012737:Sex Factors; D013806:Theophylline / Q000097:blood
D018076:DNA, Complementary; D015345:Oligonucleotide Probes; D012333:RNA, Messenger; D000082:Acetaminophen; D002110:Caffeine; D013806:Theophylline; D019363:Cytochrome P-450 CYP1A1; D019388:Cytochrome P-450 CYP1A2; C021183:1,7-dimethylxanthine