Depression of the hepatic cytochrome P450 by an acute inflammatory reaction: characterization of the nature of mediators in human and rabbit serum, and in the liver

Role of nitric oxide in downregulation of cytochrome P450 1a1 and NADPH: Quinone oxidoreductase 1 by tumor necrosis factor-alpha and lipopolysaccharide

We previously demonstrated that tumor necrosis factor alpha (TNF-alpha) and lipopolysaccharide (LPS) downregulate aryl hydrocarbon receptor (AhR)-regulated genes, such as cytochrome P450 1a1 (Cyp1a1) and NADPH: quinone oxidoreductase 1 (Nqo1) gene expression, yet the mechanisms involved remain unknown. The correlation between the inflammation-mediated suppression of AhR-regulated genes and the TNF-alpha or LPS-induced nitric oxide (NO) production especially in murine hepatoma Hepa 1c1c7 cells has been questioned; therefore we investigated whether NO is involved in the modulation of Cyp1a1 and Nqo1 by TNF-alpha or LPS in Hepa 1c1c7 cells. A significant dose-dependent increase in the inducible nitric oxide synthase (NOS2) expression and NO production were observed by various concentrations of TNF-alpha (1, 5, and 10 ng/mL) and LPS (1 and 5 microg/mL) which was completely inhibited by a NOS2 inhibitor, L-N6-(1-iminoethyl) lysine (L-NIL) (1 mM). Furthermore, TNF-alpha and LPS significantly induced NOS2 expression. Both TNF-alpha and LPS repressed the beta-naphthoflavone (betaNF)-mediated induction of Cyp1a1 and Nqo1 at mRNA and activity levels. The downregulation of Cyp1a1, but not Nqo1, was significantly prevented by L-NIL. However, proxynitrite decomposer, iron tetrakis (N-methyl-4'-pyridyl) porphyrinato (FeTMPyP) (5 microM) did not affect TNF-alpha- and LPS-mediated downregulation of Cyp1a1 and Nqo1 at mRNA and activity levels. These results show that NO, but not peroxynitrite, may be involved in TNF-alpha- and LPS-mediated downregulation of Cyp1a1 without affecting the downregulation of Nqo1.

The effects of diabetes with hyperlipidemia on P450 expression in APA hamster livers

The effect of chronic hyperglycemia and hyperlipidemia induced by streptozotocin (SZ) on the expression of P450 in the liver of APA hamsters was studied in this experiment. No effect on the total activity of P450 was seen in SZ-induced diabetic hamsters throughout the experimental period. At 1 and 6 months after SZ-injection, the levels of CYP1A, 2C6, and 3A of SZ-injected hamsters were much lower than those of age-matched control hamsters. CYP2B expression tended to decrease and CYP2E1 and 4A expression tended to increase in SZ-injected hamsters, although the results were not significant. At 3 months after SZ-injection, however, no significant difference between SZ-injected and normal hamsters was seen in these P450 isozymes. On the other hand, CYP2C11 expression was slightly depressed in SZ1M and SZ6M, and almost equivalent to control hamsters in SZ3M. Immunohistochemistry by the use of each isozyme antibody revealed that SZ-induced diabetes affected the localization of CYP2C6, 3A, and 4A in the hepatic acinus. The expression of CYP2C6 and 3A was depressed mainly in the periportal region of the acinus, and CYP4A expression was induced mainly in the perivenous region by SZ-induced diabetes. On the other hand, the expression pattern of CYP1A, 2B, 2C11, and 2E1 were not affected. These results demonstrate that the effects of SZ-induced diabetes on hepatic P450 differ for each isozyme in APA hamsters and also differ from those of other experimental diabetic animals, including golden hamsters.

Alteration of drug biotransformation and elimination during infection and inflammation

During infection or inflammation, the expression of cytochrome P450 and its dependent biotransformation pathways are modified. This results in a change in the capacity of the liver to handle drugs and in alterations in the production and elimination of endogenous substances throughout the body. The majority of the CYP isoforms are modified at pre-translational steps in protein synthesis, and, in most cases, cytokines are involved as mediators of the response. Recent information suggests that inflammatory responses that are localized to the CNS cause a loss of CYP within the brain. This is accompanied by a parallel down-regulation of CYP in peripheral organs that is mediated by a signaling pathway between the brain and periphery. This review covers the loss that occurs in the major mammalian CYP families in response to infection/inflammation and the mediator pathways that are key to this response.

Effect of hypoxia alone or combined with inflammation and 3-methylcholanthrene on hepatic cytochrome P450 in conscious rabbits

1 To investigate the effect of moderate hypoxia alone or combined with an inflammatory reaction or after 3-methylcholanthrene (3MC) pre-treatment on cytochrome P450 (P450), conscious rabbits were exposed for 24 h to a fractional concentration of inspired O2 of 10% (mean PaO2 of 34 mmHg). Hypoxia decreased theophylline metabolic clearance (ClM) from 1.73+/-0.43 to 1.48+/-0.13 ml min-1 kg-1 (P<0. 05), and reduced (P<0.05) the formation clearance of theophylline metabolites, 3-methylxanthine (3MX), 1-methyluric acid (1MU) and 1,3-dimethyluric acid (1,3DMU). Hypoxia reduced the amount of CYP1A1 and 1A2 but increased CYP3A6 proteins. 2 Turpentine-induced inflammatory reaction reduced (P<0.05) the formation clearance of 3MX, 1MU, and 1,3DMU, and diminished the amount of CYP1A1, 1A2 and 3A6 proteins. However, when combined with hypoxia, inflammation partially prevented the decrease in ClM, especially by impeding the reduction of 1,3DMU. The amount of CYP1A1 and 1A2 remained reduced but the amount of CYP3A6 protein returned to normal values. 3 Pre-treatment with 3MC augmented the ClM by 114% (P<0.05) due to the increase in the formation clearance of 3MX, 1MU and 1,3DMU. 3MC treatment increased the amount of CYP1A1 and 1A2 proteins. Pre-treatment with 3MC prevented the hypoxia-induced decrease in amount and activity of the P450. 4 It is concluded that acute moderate hypoxia and an inflammatory reaction individually reduce the amount and activity of selected apoproteins of the P450. However, the combination of hypoxia and the inflammatory reaction restores P450 activity to near normal values. On the other hand, pre-treatment with 3MC prevents the hypoxia-induced depression of the P450.