Hepatic disposition and effects of nitric oxide donors: rapid and concentration-dependent reduction in the cytochrome P450-mediated drug metabolism in isolated perfused rat livers.
Inflammatory reactions reduce the activity of cytochrome P450 isoforms. The aim of the study was to determine the mechanisms underlying the decrease in CYP1A2 and CYP3A6 catalytic activities produced by serum from rabbits with a turpentine-induced inflammatory reaction (STIIR) and interleukin 6 (IL-6). STIIR and IL-6 were incubated with cultured primary hepatocytes from control rabbits (HCONT), and from rabbits with a turpentine-induced inflammatory reaction (HTIIR) in the absence or presence of pyrrolidine dithiocarbamate (PDTC), an antioxidant and inhibitor of nuclear factor B transcription; 2 -amino-3 -methoxyflavone (PD98059), an inhibitor of extracellular signal-related kinase (Erk1/2); 4-(4-fluorophenyl)2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB203580), an inhibitor of p38MAPK; N -nitro-L-arginine methyl ester, an inhibitor of nitric-oxide synthase 2 (NOS2); the combination of PDTC, PD98059, and SB203580; and genistein, an inhibitor of Janus-associated protein tyrosine kinase (JAK). After 4 and 24 h of incubation of HCONT with STIIR and IL-6, CYP1A2 activity was reduced without changes in expression; the reduction in activity was partially prevented by the inhibition of JAK, Erk1/2, and NOS2. In HCONT, STIIR and IL-6 did not affect CYP3A6 activity; however, PDTC reduced CYP3A6 activity by 40 and 80% after 4 and 24 h of incubation. In HTIIR, STIIR and IL-6 reduced both CYP1A2 and CYP3A6 activities; this decrease is partially prevented by inhibitors of protein tyrosine kinases, Erk1/2, and NOS2. In HTIIR, SB203580 increased CYP3A6 activity in a dose-dependent manner without changes in protein expression. These results show that the signal transduction pathways mediating the decrease in CYP1A2 and 3A6 activity, produced by STIIR and IL-6, involve JAK, Erk1/2, and NOS2. There is considerable evidence that in humans an inflammatory reaction can diminish the activity of the cytochrome P450 (P450) superfamily . The first documented observation reported that an upper respiratory viral infection in asthmatic children increased theophylline plasma concentrations and half-life (Chang et al., 1978). Actually, numerous reports have documented that influenza infections reduce the rate of biotransformation of theophylline and other drugs (Cheng and Morgan, 2001; Renton, 2001). Moreover, bacterial respiratory infections, as well as chronic obstructive lung disease, reduce the ability of the organism to clear xenobiotics (Sonne et al., 1985). Other causes of inflammation, such as elective surgery, reduce the activity of CYP3A4 (Haas et al., 2003). Using animal models, it has been shown that various models of inflammation, such as the injection of lipopolysaccharide (LPS), turpentine, and carrageenan depress the activity of the P450 (Cheng and Morgan, 2001; Renton, 2001). Already in 1978, the decrease in theophylline clearance was attributed to the down-regulation of P450 isoforms (Renton, 1978). Since then, many reports have confirmed that an inflammatory reaction triggers the release of proinflammatory mediators, e.g., IL-6, IL-1 , and interferon, among others, which will cause a transcriptional down-regulation of P450 genes and post-transcriptional reductions in enzyme expression (Riddick et al., 2004). Actually, it is known that, in vivo and in vitro, the down-regulation of P450 isoforms is preceded by a decrease in activity that is mediated primarily by IL-6, IL-1 and interferon(El-Kadi et al., 1997; Bleau et al., 2000; Barakat et al., 2001). This post-translational reduction in P450 activity is still not well understood, but has been associated with reversible inhibitory effects of reactive oxygen species (ROS) and nitric oxide (NO ) (Takemura et al., 1999; El-Kadi et al., 2000), and implicates the activation of extracellular signal-related kinases (Erk1/2) and protein kinase C (Levitchi et al., 2004). It is actually emerging that the effect of an inflammatory reaction on P450 activity is enzyme-selective. Several reasons underlie such specificity: 1) the serum mediators released by inflammation, e.g., cytokines, down-regulate the expression of P450 isoforms differenThis study was supported by the Canadian Institutes of Health Research