The 2001 Veylien Henderson Award of the Society of Toxicology of Canada. Positive and negative transcriptional regulation of cytochromes P450 by polycyclic aromatic hydrocarbons

2003 ◽  
Vol 81 (1) ◽  
pp. 59-77 ◽  
Author(s):  
David S Riddick ◽  
Chunja Lee ◽  
Anahita Bhathena ◽  
Yoav E Timsit
Keyword(s):  
Growth Hormone ◽  
Transcriptional Regulation ◽  
Cytochrome P450 ◽  
Aromatic Hydrocarbon ◽  
Aromatic Hydrocarbons ◽  
Cytochromes P450 ◽  
Biological Significance ◽  
Male Rats ◽  
Cytochrome P450 1A1 ◽  
Aromatic Hydrocarbon Receptor

Most responses to aromatic hydrocarbons such as 3-methylcholanthrene (MC) and 2,3,7,8-tetrachlorodibenzo-p-dioxin are mediated by the aromatic hydrocarbon receptor (AHR). The AHR regulates induction of drug-metabolizing enzymes such as cytochrome P450 1A1. However, the expression of several genes of biological significance is decreased by these chemicals. We are examining the mechanisms by which aromatic hydrocarbons suppress constitutive hepatic cytochromes P450, especially the male-specific rat liver cytochrome P450 2C11 (CYP2C11), which is regulated by pulsatile growth hormone (GH) secretion. Aromatic hydrocarbons suppress CYP2C11 via a transcriptional mechanism both in vivo and in cultured hepatocytes, and the AHR appears to be involved; however, studies of protein–DNA interactions and reporter genes driven by the CYP2C11 5'-flanking region have not provided a definitive mechanism for this response. MC attenuates the ability of GH to stimulate hepatic CYP2C11 expression in hypophysectomized (hypx) male rats, and this prompted studies of effects of aromatic hydrocarbons on hepatic GH signaling pathways as a novel aspect of endocrine disruption. Our studies with hypx rats also suggest that the hepatic AHR protein is regulated by a pituitary factor(s). The goal of these molecular mechanistic studies is to improve our understanding of how environmental contaminants modulate the expression of genes coding for xenobiotic- and hormone-metabolizing enzymes.Key words: aromatic hydrocarbons, cytochrome P450, aromatic hydrocarbon receptor, growth hormone, transcriptional regulation.

Chicken Egg Yolk as an Excellent Source of Highly Specific Antibodies Against Cytochromes P450

2004 ◽  
Vol 69 (3) ◽  
pp. 659-673 ◽  
Author(s):  
Petr Hodek ◽  
Tomáš Koblas ◽  
Helena Rýdlová ◽  
Božena Kubíčková ◽  
Miroslav Šulc ◽  
...  
Keyword(s):  
Cytochrome P450 ◽  
Cytochromes P450 ◽  
Egg Yolk ◽  
Good Alternative ◽  
Invasive Technique ◽  
Cytochrome P450 1A1 ◽  
Orconectes Limosus ◽  
Chicken Egg ◽  
Cytochrome P450 2B4 ◽  
Human Livers

Using chicken antibodies IgY (purified from egg yolks) against mammalian cytochromes P450 and by means of cytochrome P450 marker substrates, we found for the first time the presence of hepatopancreatic cytochrome P450 in crayfishOrconectes limosus(an inducible cytochrome P450 2B-like enzyme) and we were able to detect and quantify cytochrome P450 1A1 in microsomes of human livers. Expression levels of cytochrome P450 1A1 in human livers constituted less than 0.6% of the total hepatic cytochrome P450 complement. The results obtained in our study are clear examples that chicken IgY are suitable for cytochrome P450 detection and quantification. Due to the evolutionary distance, chicken IgY reacts with more epitopes on a mammalian antigen, which gives an amplification of the signal. Moreover, this approach offers many advantages over common mammalian antibody production since chicken egg is an abundant source of antibodies (about 100 mg IgY/yolk) and the egg collection is a non-invasive technique. In the case of antibodies against cytochrome P450 2B4, we documented fast and steady production of highly specific immunoglobulins. Thus, chicken antibodies should be considered as a good alternative to and/or superior substitute for conventional polyclonal antibody produced in mammals.

Lack of mechanism-based inactivation of rat hepatic microsomal cytochromes P450 by doxorubicin

1999 ◽  
Vol 77 (8) ◽  
pp. 589-597 ◽  
Author(s):  
Johnny Di Re ◽  
Chunja Lee ◽  
David S Riddick
Keyword(s):  
Lipid Peroxidation ◽  
Cytochrome P450 ◽  
Reductase Activity ◽  
Cytochromes P450 ◽  
Microsomal Protein ◽  
Positive Control ◽  
Male Rats ◽  
Protein Levels

Administration of the antineoplastic doxorubicin to rodents causes depression of hepatic cytochrome P450 (CYP) dependent biotransformation, an effect that has been partially attributed to the ability of doxorubicin to stimulate microsomal lipid peroxidation. Since doxorubicin can be bioactivated by the CYP/NADPH-CYP reductase system to products that bind covalently to microsomal protein, we hypothesized that doxorubicin functions as a mechanism-based inactivator of hepatic microsomal CYPs and (or) NADPH-CYP reductase under conditions in which doxorubicin-stimulated NADPH-dependent lipid peroxidation is minimized. In vitro studies were conducted with hepatic microsomes isolated from untreated and phenobarbital-treated male rats. Unlike the positive control carbon tetrachloride, doxorubicin (10 µM) did not stimulate NADPH-dependent lipid peroxidation in microsomal incubations containing EDTA (1.5 mM). Doxorubicin did not cause NADPH-dependent loss of microsomal CYP, heme, or steroid hydroxylation activities selective for CYP2A, CYP2B, CYP2C11, and CYP3A. The positive control 1-aminobenzotriazole caused marked NADPH-dependent decreases in all of these parameters. Neither doxorubicin nor 1-aminobenzotriazole caused NADPH-dependent loss of NADPH-CYP reductase activity, and neither compound altered the immunoreactive protein levels of CYP2B, CYP2C11, CYP3A, and NADPH-CYP reductase. These results indicate that a pharmacologically relevant concentration of doxorubicin does not cause direct mechanism-based inactivation of hepatic microsomal CYPs or NADPH-CYP reductase, suggesting that the ability of doxorubicin to depress hepatic CYP-mediated biotransformation in vivo is due to lipid peroxidation mediated heme destruction, altered heme metabolism, and (or) decreased expression of selected CYP enzymes.Key words: doxorubicin, cytochrome P450, mechanism-based inactivation, lipid peroxidation.

Microsomal cytochrome P450 1A1 dependent monooxygenase activity in guinea pig heart: induction, inhibition, and increased activity by addition of exogenous NADPH–cytochrome P450 reductase

1993 ◽  
Vol 71 (2) ◽  
pp. 151-156 ◽  
Author(s):  
Gordon P. McCallum ◽  
Jennifer E. Horton ◽  
K. Cameron Falkner ◽  
John R. Bend
Keyword(s):  
Cytochrome P450 ◽  
Guinea Pig ◽  
Aromatic Hydrocarbon ◽  
Cytochrome P450 Reductase ◽  
Cytochrome P450 1A1 ◽  
Guinea Pig Heart ◽  
Nadph Cytochrome ◽  
P450 Reductase ◽  
Polycyclic Aromatic ◽  
Nadph Cytochrome P450 Reductase

Characterization of cytochrome P450 1A1 dependent monooxygenases in guinea pig heart revealed low rates of 7-ethoxyresorufin O-deethylation, which are markedly increased (20-fold) by treatment with β-naphthoflavone, a poly cyclic aromatic hydrocarbon. Both 7-ethoxyresorufin O-deethylation and 7-methoxyresorufin O-demethylation were found to be approximately 4-fold higher in microsomes prepared from the ventricle than the atrium of β-naphthoflavone-induced guinea pigs. The low rates of 7-ethoxyresorufin O-deethylation in cardiac microsomes were due, at least in part, to a deficiency of the flavoprotein NADPH–cytochrome P450 reductase; addition of exogenous NADPH–cytochrome P450 reductase dramatically increased 7-ethoxyresorufin O-deethylation in cardiac microsomes of guinea pigs, before and after treatment with β-naphthoflavone. N-Benzyl-1-aminobenzotriazole, a suicide substrate of cytochrome P450 1A1 in guinea pig, was able to inhibit almost all of the 7-ethoxyresorufin O-deethylase and 7-methoxyresorufin O-demethylase activities in polycyclic aromatic hydrocarbon induced guinea pig heart (88 and 71%, respectively), suggesting that cytochrome P450 1A1 coupled to NADPH–cytochrome P450 reductase in these microsomes inactivates itself by a suicidal mechanism. Addition of α-naphthoflavone, an inhibitor of cytochrome P450 1A isozymes, to cardiac microsomes from β-naphthoflavone-induced guinea pigs resulted in greater than 95% inhibition of 7-ethoxyresorufin O-deethylase activity. The biological significance of these low levels of cytochrome P450 1A1 monooxygenase activity in guinea pig heart and their induction by polycyclic aromatic hydrocarbons are not currently understood.Key words: guinea pig, heart, cytochrome P450, NADPH–cytochrome P450 reductase, polycyclic aromatic hydrocarbon.

scholarly journals Early expression of requisite developmental growth hormone imprinted cytochromes P450 and dependent transcription factors

2021 ◽  
Vol 10 (9) ◽  
pp. 1167-1179
Author(s):  
Sarmistha Banerjee ◽  
Allison M Hayes ◽  
Bernard H Shapiro
Keyword(s):  
Growth Hormone ◽  
Sex Differences ◽  
Cytochromes P450 ◽  
Signal Transduction Pathway ◽  
Male Rats ◽  
Adult Health ◽  
Gh Secretion ◽  
Metabolic Functions ◽  
Sexually Dimorphic Expression ◽  
Early Expression

The sexually dimorphic expression of cytochromes P450 (CYP) drug metabolizing enzymes has been reported in all species examined. These sex differences are initially expressed during puberty and are solely regulated by sex differences in the circulating growth hormone (GH) profiles. Once established, however, the different male- and female-dependent CYP isoforms are permanent and immutable, suggesting that adult CYP expression requires imprinting. Since the hormone that regulates an adult function is likely the same hormone that imprints the function, we selectively blocked GH secretion in some newborn male rats while others also received a concurrent physiologic replacement of rat GH. Rats were subsequently challenged, peripubertally, with either a masculine-like episodic GH regimen or the GH vehicle alone. The results demonstrate that episodic GH regulation of male-specific CYP2C11 and CYP3A2, as well as female-predominant CYP2C6, are dependent on developmental GH imprinting. Moreover, the induction and/or activation of major components in the signal transduction pathway regulating the expression of the principal CYP2C11 isoform is obligatorily dependent on perinatal GH imprinting without which CYP2C11 and drug metabolism would be permanently and profoundly suppressed. Since there are additional adult metabolic functions also regulated by GH, pediatric drug therapy that is known to disrupt GH secretion could unintentionally impair adult health.

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