Induction of Cytochrome P450 1A5 mRNA, Protein and Enzymatic Activities by Dioxin-Like Compounds, and Congener-Specific Metabolism and Sequestration in the Liver of Wild Jungle Crow (Corvus macrorhynchos) from Tokyo, Japan

Abstract

This study presents concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and dioxin-like coplanar PCBs (Co-PCBs) in the liver and breast muscle of jungle crows (JCs; Corvus macrorhynchos) collected from Tokyo, Japan. 2,3,7,8-Tetrachlorodibenzo-p-dioxin toxic equivalents (TEQs) derived by WHO bird-TEF were in the range of 23 to 280 pg/g (lipid) in the liver, which are lower or comparable to the lowest-observed-effect-level of CYP induction in chicken, and 5.6-78 pg/g (lipid) in the pectoral muscle. Cytochrome P450 (CYP) 1A-, 2B-, 2C-, and 3A-like proteins were detected using anti-rat CYP polyclonal antibodies in hepatic microsomal fractions. Significant (p < 0.05) positive correlations between hepatic TEQs and CYP1A or CYP3A-like protein expression levels were noticed, implying induction of these CYP isozymes by TEQs. On the other hand, there was no significant positive correlation between muscle TEQ and any one of analyzed CYP isozyme expression levels. CYP1A- and CYP3A-like protein expression levels represented better correlations with pentoxy- and benzyloxyresorufin-O-dealkylase activities rather than methoxy- and ethoxyresorufin-O-dealkylase activities, indicating unique catalytic functions of these CYPs in JCs. Furthermore, we succeeded in isolating CYP1A5 cDNA from the liver of JC, having an open reading frame of 531 amino acid residues with a predicted molecular mass of 60.3 kDa. JC CYP1A5 mRNA expression measured by real-time RT-PCR had a significant positive correlation with hepatic TEQs, suggesting induction of CYP1A5 at the transcriptional level. Ratios of several Co-PCB congeners to CB-169 in the liver of JCs revealed significant negative correlations with CYP1A protein or CYP1A5 mRNA expression levels, implying metabolism of these congeners by the induced CYP1A. The liver/breast muscle concentration (L/M) ratios of PCDDs/DFs and CB-169 increased with an increase in hepatic CYP1A protein or CYP1A5 mRNA expression levels, suggesting congener-specific hepatic sequestrations by the induced CYP1A. The present study provides insights into the propensity of CYP1A induction to the exposure of dioxin-like chemicals, and unique metabolic and sequestration capacities of CYP1A in JC.

Dioxin‐like and perfluorinated compounds in pigs in an Indian open waste dumping site: Toxicokinetics and effects on hepatic cytochrome P450 and blood plasma hormones

“…The concentration ratios of certain congeners (congener x/PCB169) had negative correlations with CYP1A-like protein content, possibly as a result of preferential metabolism, as reported for some other species [14,15,40]. In pigs, the concentration ratio of PCB114 showed a significant negative correlation with CYP1A-like protein levels (r ¼ À0.44, p < 0.05).…”

“…Interspecies comparison of the L/A (or liver-to-muscle) ratios showed that the capacity for hepatic sequestration of DRCs in pigs was comparable to that in the raccoon dog [16] but higher than the capacities in the Baikal seal [12], common cormorant [13], and jungle crow [15].…”

Effects of pentachlorophenol on the detoxification system in white-rumped munia ( Lonchura striata )

“…Alkoxyresorufin O-dealkylase (AROD) activities, including EROD, MROD and BROD activities, are typical catalytic markers for a variety of CYP450 enzymes, and thus have great potential to elucidate CYP450 induction by chemical exposure. Among them, EROD activity has been used extensively as a sensitive indicator of the effects of exogenous compounds on CYP1A induction in avian species (Kubota et al, 2006;Verbrugge et al, 2001;Watanabe et al, 2005). Our study revealed that PCP increased EROD activity in the 0.5 mg/(kg·day) PCP exposure group (p < 0.05) (Fig.…”

CYP1A in TCDD Toxicity and in Physiology–with Particular Reference to CYP Dependent Arachidonic Acid Metabolism and other Endogenous Substrates

“…CYP1A5, the avian CYP1A2 ortholog, also selectively binds and sequesters PCBs (Watanabe et al, 2005). Interestingly, non-halogenated hydrocarbon CYP1A inducers may not be subject to CYP1A2 sequestration, as evidenced by a lack of sequestration for indole-3-carbinol, a tryptophan related AhR ligand (Anderton et al, 2004).…”