Rapid Transcriptional Suppression of Rat Cytochrome P450 Genes by Endotoxin Treatment and Its Inhibition by Curcumin

Down-regulation of constitutive hepatic cytochrome P450 (P450) mRNAs by bacterial endotoxin (lipopolysaccharide, LPS) or other inflammatory stimuli has been documented extensively, but the contribution of transcriptional suppression to this effect is poorly understood. Here, we demonstrate that the rates of transcription of the CYP2C11, CYP3A2, and CYP2E1 genes are reduced to 20, 30, and 10% of control levels, respectively, in rat liver within 1 to 2 h of injection of LPS (1 mg/kg). The magnitude and rapidity of these effects indicate that transcriptional suppression is a primary reason for the decline in P450 mRNAs. Injection of curcumin significantly inhibited the rapid transcriptional suppression of CYP2E1, and blocked that of CYP3A2. These effects seemed to be independent of inhibition of nuclear factor-kappaB (NF-kappaB) activation by curcumin, because induction of known NF-kappaB-regulated genes was not attenuated. One hour after LPS injection, the DNA-binding activities of hepatocyte nuclear factor (HNF)1alpha, HNF3beta, and HNF4alpha were reduced to 73, 72, and 53%, respectively, of control values. The nuclear abundances of Sp1, liver-enriched transcriptional inhibitory protein (LIP), HNF1alpha, and HNF3beta were unchanged, whereas the abundance of HNF4alpha was reduced to 87% of control levels. We conclude that changes in Sp1 or LIP do not contribute significantly to the early suppression of P450 transcription in the acute phase rat liver. Although changes in DNA-binding activities of HNF1alpha, HNF3beta, and HNF4alpha are too small individually to explain the observed changes in P450 transcription, the role of each factor in concert with other factors remains to be determined.