tert-BUTYLHYDROQUINONE IS A NOVEL ARYL HYDROCARBON RECEPTOR LIGAND

Abstract

ABSTRACT:In contrast to the beneficial effects of tert-butylhydroquinone (tBHQ) as a food antioxidant, a number of studies have shown that chronic exposure to tBHQ may induce carcinogenicity. Therefore, we examined the ability of tBHQ to induce the cytochrome P450 1a1 (Cyp1a1), an enzyme known to play an important role in the chemical activation of xenobiotics to carcinogenic derivatives. A significant concentration-dependent increase in Cyp1a1 mRNA, protein, and activity occurred after treatment of murine hepatoma Hepa 1c1c7 cells with tBHQ. The increase in mRNA was apparent 3 h after treatment. The RNA polymerase inhibitor, actinomycin D, completely blocked the Cyp1a1 induction by tBHQ, indicating a requirement of de novo RNA synthesis through transcriptional activation. The protein synthesis inhibitor cycloheximide superinduced the tBHQ-mediated induction of Cyp1a1 mRNA and completely prevented the increase in Cyp1a1 activity, indicating that the induction of enzyme activity by tBHQ is dependent on de novo protein synthesis. In addition, the aryl hydrocarbon receptor (AHR) antagonist, resveratrol, inhibited the increase in Cyp1a1 activity by tBHQ. Gel electrophoretic mobility shift assays showed that tBHQ causes activation or transformation of the AHR in nuclear extracts, indicating that AHR-dependent mechanisms contributed to the Cyp1a1 induction. Similar to murine Hepa 1c1c7 cells, tBHQ caused a concentration-dependent increase in CYP1A1 at the mRNA and activity levels in human HepG2 cells. This is the first demonstration that the phenolic antioxidant, tBHQ, can directly induce Cyp1a1 gene expression in an AHR-dependent manner and may represent a novel mechanism by which tBHQ promotes carcinogenicity.

REGULATION OFCYP1A1GENE EXPRESSION BY THE ANTIOXIDANTTERT-BUTYLHYDROQUINONE

“…Combined TCDD/tBHQ treatment of HepG2 cells led to a decrease in all the parameters measured (DRE reporter activity, CYP1A1 mRNA expression, and CYP1A activity) when compared with values obtained with TCDD alone. tBHQ has been shown to bind and activate the AhR (Gharavi and El-Kadi, 2005). However, it may behave as a partial agonist that, when present at a very high concen- tration compared with TCDD, may lower the maximal achievable inducing effect of the latter.…”

“…This study was initiated because we had previously observed that phenolic antioxidants can induce human UDPglucuronosyltransferase 1A6 by a mechanism in which DRE binding of the AhR plays some role (Münzel et al, 2003). Moreover, two recent studies report on an inducing effect of tBHQ on CYP1A1 in HepG2 cells (Sugatani et al, 2004) and Hepa1c1c7 cells (Gharavi and El-Kadi, 2005).…”

Determination of the Dominant Arachidonic Acid Cytochrome P450 Monooxygenases in Rat Heart, Lung, Kidney, and Liver: Protein Expression and Metabolite Kinetics

“…To determine the protein expression pattern of the main P450 epoxygenases, CYP2Bs, CYP2C11, CYP2C23, and CYP2J3, and the main P450 hydroxylases, CYP4As, and CYP4Fs for each organ, Western blot analysis was performed using a previously described method (26). Briefly, 5-40 μg of heart, lung, kidney, and liver microsomal preparations were separated by 10% sodium dodecyl sulfate-polyacrylamide gel (SDS-PAGE), and then electrophoretically transferred to nitrocellulose membrane.…”

An Overview on Applications and Side Effects of Antioxidant Food Additives

“…Accordingly, none of these antioxidants can be used in food for infants and children. Prolonged exposure to very high doses of TBHQ may also be carcinogenic (Gharavi and Kadi, 2005). However, the European Food Safety Agency (EFSA) reported that TBHQ is a safe food additive if only authorized doses are applied to foodstuff (Scientific Opinion, 2004Race, 2009).…”