Enhanced Induction of Cytochrome P450 Enzymes and CAR Binding in TNF (p55^−/−/p75^−/−) Double Receptor Knockout Mice Following Phenobarbital Treatment

Abstract

Phenobarbital (PB) is a well characterized inducer of cytochrome P450 (P450) 2B and 3A subfamilies. Several proinflammatory cytokines have been shown to negatively modulate the induction of P450 by PB. In addition, PB is known to elicit an inflammatory mitogenic effect on the liver. To date, no studies have evaluated the PB induction profile of hepatic P450 in the absence of an intact tumor necrosis factor-alpha (TNF␣) response. To test the hypothesis that endogenous TNF␣ signaling modulates hepatic P450 induction by PB in vivo, PB induction was examined in TNF (p55 Ϫ/Ϫ /p75 Ϫ/Ϫ ) double receptor knockout mice (ko-TNF) and wild-type mice (wt-TNF). CYP2B-and CYP3A-associated activities and protein content were induced to a significantly greater extent (p Ͻ 0.05) in ko-TNF mice compared with wt-TNF mice. In parallel with enhanced CYP2B induction, an apparent elevation in the nuclear accumulation of the principal regulatory protein for transcription of CYP2B genes, the constitutively activated receptor (CAR), was detected in ko-TNF nuclear extracts following PB treatment. Additionally, nuclear factor -B binding was induced by PB in wt-TNF mice, but not in ko-TNF mice, indicating that the hepatic inflammatory response following PB treatment differed between wt-TNF and ko-TNF mice. These data demonstrate that endogenous TNF␣ signaling modulates PB induction of hepatic CYP2B and CYP3A isoforms in vivo. Further, the data presented herein suggest that endogenous TNF␣ signaling influences PB induction of CYP2B through inhibition of CAR nuclear accumulation.

The Sterolgene v0 cDNA microarray: a systemic approach to studies of cholesterol homeostasis and drug metabolism

“…In TNF-α treated fasted mice we observe up-regulation of cholesterol biosynthesis ( Cyp51a1 , Sc4mol ) and down-regulation of cholesterol excretion ( Cyp8b1 ) (Table 2 ). However, drug metabolism is further repressed ( Cyp2f2 , Cyp2j5 , Cyp3a25 ) and this also has previously been shown [ 16 ]. Two up-regulated ( Cyp51a1 , Sc4mol ) and one down-regulated gene ( Cyp8b1 ) from cholesterol homeostasis have been confirmed by RT-PCR [ 15 ] (Figure 4B ).…”

The Nuclear Factor-κB Pathway Regulates Cytochrome P450 3A4 Protein Stability

“…As a result, P450 enzymes can be a significant source of intracellular oxidative stress (Zangar et al, 2004). Consistent with its role as a regulator of intracellular oxidative stress, NF-B is known to interact with a variety of transcriptional factors that regulate P450 expression, including the pregnane X receptor, the constitutively active receptor, and the aryl hydrocarbon receptor (Tian et al, 2002;Van Ess et al, 2002;Gu et al, 2006;Zhou et al, 2006). In this study, however, analysis of CYP3A4 mRNA levels indicates that just the opposite is true.…”

Expression of c-jun is not mandatory for mouse hepatocyte proliferation induced by two nuclear receptor ligands: TCPOBOP and T3

“…An inhibitory effect on nuclear receptor expression and activity is also exerted by endogenous expression of pro-inflammatory cytokines following nuclear receptor ligand administration [21]. Indeed, (i) treatment of TNFR-double receptor KO mice with the CAR agonist PB is associated with an increased transcriptional activation of this nuclear receptor [21], and, (ii) hepatocyte proliferation after TCPOBOP occurs at a higher rate in TNFR1 À/À or double TNFR1 À/À TNFR2 À/À mice [22].…”

“…An inhibitory effect on nuclear receptor expression and activity is also exerted by endogenous expression of pro-inflammatory cytokines following nuclear receptor ligand administration [21]. Indeed, (i) treatment of TNFR-double receptor KO mice with the CAR agonist PB is associated with an increased transcriptional activation of this nuclear receptor [21], and, (ii) hepatocyte proliferation after TCPOBOP occurs at a higher rate in TNFR1 À/À or double TNFR1 À/À TNFR2 À/À mice [22]. A negative cross-talk between CAR and JNK pathway is also evident from recent studies showing that (i) CAR acts as a negative regulator of JNK by forming a complex with MEKK7 through its co-activator GADD45b [23] and (ii) loss of GADD45b is associated with selective overactivation of the MEKK/JNK pathway [24].…”