ToxSci Advance Access originally published online on March 22, 2007
Toxicological Sciences 2007 97(2):318-335; doi:10.1093/toxsci/kfm066
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Molecular Characterization of Cytochrome P450 1A1, 1A2, and 1B1, and Effects of Polychlorinated Dibenzo-p-dioxin, Dibenzofuran, and Biphenyl Congeners on Their Hepatic Expression in Baikal Seal (Pusa sibirica)
* Center for Marine Environmental Studies, Ehime University, Bunkyo-cho 2-5, Matsuyama 790-8577, Japan
Department of Animal Sciences, Teikyo University of Science and Technology, 2525 Yatsusawa, Uenohara 409-0193, Japan
Center for International Cooperation, Ocean Research Institute, The University of Tokyo, Minamidai 1-15-1, Nakano-ku Tokyo 164-8639, Japan
The Eastern-Siberian Scientific and Production Fisheries Center, Hakhalov st. 4, Ulan-Ude, Buryatia, 670034, Russia
1 To whom correspondence should be addressed. Fax: +81-89-927-8172. E-mail: iwatah{at}agr.ehime-u.ac.jp.
Received January 14, 2007; accepted March 16, 2007
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Abstract |
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This study attempts to relate the 2,3,7,8-tetrachlorodibenzo-p-dioxin toxic equivalent (TEQ) level with certain responses including the catalytic activities and expression of hepatic cytochrome P450 (CYP) 1A and CYP1B in wild population of Baikal seal (Pusa sibirica). We isolated full-length CYP1A1, 1A2, and 1B1 cDNAs, which encode proteins of 516, 512, and 543 amino acids, respectively. Immunochemical analysis demonstrated that a cross-reactive protein with polyclonal antibody against rat CYP1A1 or CYP1B1 was detected in the seal liver. Total TEQ levels showed significant positive correlations with expression levels of CYP1A1, 1A2, and 1B1 mRNAs, and further with both CYP1A- and CYP1B-like proteins, indicating chronic induction of these CYP isozymes by TEQs. The 50% effective concentration for CYP1A-like protein induction was estimated to be 65 pg TEQ/g wet weight. To evaluate the potential of congener-specific metabolism, profiles of negative correlations between the concentrations of eachcongener normalized to a relatively recalcitrant congener, PCB169, and CYP1A-like protein levels were also estimated. Significant negative correlations of 2,3,7,8-tetrachlorodibenzofuran and PCB77 to CYP1A-like protein expression may possibly be due to the preferential metabolism of these congeners. Anti-rat CYP1A1 and CYP1B1 antisera equivalently inhibited ethoxyresorufin O-deethylase (EROD) activity in the seal microsomes, suggesting that both CYPs are involved in EROD activity. Hepatic EROD revealed an increasing trend at lower TEQs, but a declining trend at higher levels, implying a catalytic inhibition of CYP1A and CYP1B. Furthermore, ratios of CYP1B1/CYP1A1 mRNA expression levels increased with TEQs, indicating the enhanced risk of carcinogenicity by preferential induction of CYP1B1 by TEQs in the liver.
Key Words: Baikal seal; toxic equivalent; cytochrome P450 1A; cytochrome P450 1B; catalytic inhibition.