Barker, Charles W.
Suppression of cytochrome P4501A (CYP1A1 and CYP1A2) mRNA levels in isolated hepatocytes by IL-1 and oxidative stress.

Order No. 9421867

Animals subjected to immunostimulatory conditions exhibit reduced tissue levels of total CYP and CYP dependent drug metabolism. We have investigated the possibility that depressed levels of two carcinogen-metabolizing CYP enzymes may be due to decreased levels of the mRNAs encoding these enzymes by studying the effect of monocyte-derived cytokines on the induction of CYP1A1 and CYP1A2 mRNAs in isolated rat hepatocytes. Medium conditioned by activated human peripheral blood monocytes or by the U937 monocyte cell line suppressed the induction of both mRNAs by TCDD, while beta-fibrinogen mRNA levels increased 30- to 40-fold. Recombinant interleukin-1 suppressed the inducer-dependent accumulation of both CYP1A1 and CYP1A2 mRNAs in a dose-dependent fashion, while two other monocyte derived cytokines, interleukin-6 and transforming growth factor-beta, did not. Run-on transcription analysis demonstrated that conditioned medium and interleukin-1 rapidly suppressed the transcription rate of CYP1A1 and CYP1A2 in inducer-treated hepatocytes. Since many of the actions of inflammatory mediators can be mimicked by oxidative stress, we also treated isolated hepatocytes with various concentrations of H(sub 2) O(sub 2) (0.25 to 1.0 mM) to investigate the possibility that expression of these genes may also be modulated by oxidative stress. Inducer-dependent accumulation of CYP1A1 and CYP1A2 mRNAs were maximally reduced approximately 50 and 70% respectively by 1.0 mM H(sub 2) O(sub 2). Run on transcription analysis suggested that the effect of H(sub 2) O(sub 2) on these mRNAs was mediated transcriptionally. The reduction in CYP1A mRNA levels was not due to a reduction in the levels of all mRNAs due to some general toxic effect since glyceraldehyde-3-phosphate dehydrogenase, alpha-tubulin, beta- fibrinogen and albumin mRNA levels did not change or were actually increased, and lactate dehydrogenase released into the medium was not increased, with H(sub 2) O(sub 2) treatment. Insulin also reduced the expression of both mRNAs, and N- acetylcysteine, which increases intracellular glutathione levels, completely reversed the insulin effect on both mRNAs and the H(sub 2) O(sub 2) effect on CYP1A1 mRNA but only partially reversed the H(sub 2) O(sub 2) effect on CYP1A2 mRNA. Source: DAI, 55, no. 04B, (1994): 1294


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