During the host response to
During the host response to inflammation, inflammatory mediators, including release of pro-inflammatory cytokines, have been associated with altered content, expression, and activity of CYP450 enzymes, consequently leading to alterations in the metabolism and elimination of certain drugs. The losses in drug metabolism are channeled predominantly through the production of cytokines, which modify the expression and function of specific transcription factors that regulate CYP450 gene expression, i.e. Nuclear Factor-Kappa B (NF-κB). Several studies have demonstrated that the activities of many hepatic CYP450 3466 in experimental models of liver inflammation or infection and in man are down-regulated, which can cause dose-dependent drug toxicity associated with impaired in vivo drug clearance.19, 20 In most cases, the decreased activity is accompanied or preceded by decreased hepatic levels of the corresponding CYP450 mRNA and protein expression. Although, the different models of inflammation can result in different rates of drug clearance and or reduced microsomal metabolism of drugs. There is evidence for both transcriptional and post-transcriptional down-regulation of CYP450 mRNA by inflammatory stimuli. For example, the down-regulation of CYP2C11 following treatment with bacterial LPS or other inflammatory responses has been shown to primarily occur via decreased mRNA expression, which is followed by a similar decrease in protein levels.6, 23, 24 The CYP2C11 promoter contains an NF-kB binding site and mutation of the promoter prevented IL-1-mediated CYP2C11 suppression. Other proposed mechanisms that apply to specific CYP450 enzymes involve post-translational modifications or increased degradation. CYP2E1 has been shown to be most affected by inflammation at the protein level,26, 27 through mechanisms to prevent degradation, i.e. protein stabilization.28, 29, 30, 31 In the current study, the finding that CYP2E1 protein expression was restored to normal, suggests that CYP2E1 protein is stabilized or its degradation was prevented by treprostinil. Additional studies are required to elucidate the mechanisms involved. Also, the different patterns of CYP2C11 mRNA expression and activity support the idea that different inflammatory mediators regulate CYP450 expression and are enzyme-specific. Inhibition of pro-inflammatory cytokines is a major pathway responsible for the improved hepatic CYP450 expression and activity in the treprostinil-treated group. Administration of LPS is a classic model of bacterial sepsis, however, different concentrations of LPS and cytokines administered in vivo or in vitro can have enzyme-selective effects on CYP450 expression.6, 32 In a model of cold graft storage followed by reperfusion using a recirculation method, Izuishi et al examined the effects of prolonged cold graft storage on CYP450 content, protein and activity. Significant changes were observed only after 48 h of cold storage, which is not clinically feasible. In a rat model of partial ischemia (70%), 1 h of warm ischemia followed by 3 h reperfusion resulted in no significant changes in CYP2E1 or CYP2C11 protein, while CYP3A2, CYP2E1, and CYP2C11, activity decreased by 30%, 17%, and 34%.5, 33, 34 In a porcine model of warm ischemia, after 6 h of partial hepatic occlusion, the activities of CYP3A, CYP2E1, and CYP2C were decreased to 31%, 62%, and 62%, respectively, while CYP3A protein expression remained unchanged. Recently, Aguilar-Melero et al showed reduced liver I/R injury by cardiotropin-1 administration to donor pigs. Considering the various models used in these studies, it is difficult to translate the results from a model of warm partial I/R injury or a liver graft reperfused ex vivo to the clinical setting, which involves cold ischemia of a finite time period and followed by warm reperfusion, thereby invoking different cellular injuries and, consequently, different patterns of CYP450 expression in the host response. The patterns of mRNA expression, protein levels and CYP450 activity in the present study support the theory that different inflammatory mediators regulate CYP450 expression at different levels and are enzyme-specific, depending on source of injury.