Down-Regulation of the Expression of Three Major Rat Liver Cytochrome P450S by Endotoxin In Vivo Occurs Independently of Nitric Oxide Production1
- 1Department of Pharmacology, Emory University School of Medicine (M.B.S., E.T.M.); 2Program in Molecular Therapeutics and Toxicology, Graduate Division of Biological and Biomedical Sciences, Emory University (M.B.S.), Atlanta, Georgia
Abstract
Endotoxemia results in both the down-regulation of multiple cytochrome P450 genes and the induction of inducible nitric oxide synthase (NOS2). The nitric oxide (NO) released during inflammation has been implicated as the mediator of the decreased catalytic activity and expression of several cytochrome P450 isozymes. We examined the role of NO in the decreases of both gene expression and activity of three major P450s in the endotoxemic Fischer 344 rat. Endotoxin (LPS) treatment suppressed both mRNA and protein expression of P450 2C11, 2E1, and 3A2. Coadministration of the NOS inhibitor aminoguanidine to LPS-treated rats completely inhibited the release of NO into the plasma but did not reverse the down-regulation of expression of any of the P450s examined at three time points. LPS treatment had a biphasic effect on some P450 catalytic activities. The hydroxylation of testosterone at the 2α-, 16α- and to a lesser extent 6β-positions, was inhibited 6 hr after LPS treatment and returned to normal by 12 hr. The role of NO in the 6 hr effects could not be assessed due to effects of the aminoguanidine treatment itself. The second phase of decreased P450 activities seen after 24 hr was attributed to the NO-independent decrease in gene expression. Our results suggest that NO is not required for the LPS-evoked down-regulation of P450 2C11, 2E1 and 3A2 mRNA or protein expression. We cannot rule out a possible role for NO in the decreases in P450 activities seen early in the response.
Footnotes
-
Send reprint requests to: Dr. Edward T. Morgan, Department of Pharmacology, Emory University School of Medicine, 5119 Rollins Research Center, Emory University, Atlanta, GA 30322-3090.
-
↵1 This work was supported by Grants GM46897 from the National Institute of General Medical Sciences (E.T.M.) and by a Howard Hughes Predoctoral Fellowship (M.B.S.). Presented in part at the American Society for Biochemistry and Molecular Biology conference in August 1997 (San Francisco, CA).
- Abbreviations:
- LPS
- bacterial endotoxin
- IL
- interleukin
- TNF
- tumor necrosis factor
- IFN
- interferons
- NOS2
- inducible nitric oxide synthase
- NO
- nitric oxide
- GAP
- glyceraldehyde-3-phosphate dehydrogenase
- AG
- aminoguanidine
- NOx
- nitrate plus nitrite
- L-NAME
- NG-nitro-l-arginine methyl ester
-
- Received January 7, 1998.
- Accepted April 27, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
