Abstract
Most drugs and xenobiotics are metabolized in the liver. Amongst others, different cytochrome P450 (CYP) enzymes catalyze the metabolic conversion of foreign compounds, and various transport proteins are engaged in the excretion of metabolites from the hepatocytes. Inter-species and inter-individual differences in the hepatic levels and activities of drug-metabolizing enzymes and transporters result from genetic as well as from environmental factors, and play a decisive role in determining the pharmacokinetic properties of a compound in a given test system. To allow for a meaningful comparison of results from metabolism studies, it is, therefore, of utmost importance to know about the specific metabolic properties of the test systems, especially about the levels of metabolic enzymes such as the CYPs. Using a targeted proteomics approach, we, therefore, compared the hepatic levels of important CYP enzymes and transporters in different experimental systems in vivo and in vitro, namely Wistar rats, C57/Bl6 mice, mice humanized for the two xeno-sensing receptors PXR (pregnane-X-receptor) and CAR (constitutive androstane receptor), mice with human hepatocyte-repopulated livers, human HepaRG hepatocarcinoma cells, primary human hepatocytes, and human liver biopsies. In addition, the effects of xenobiotic inducers of drug metabolism on CYP enzymes and transporters were analyzed in selected systems. This study for the first time presents a comprehensive overview of similarities and differences in important drug metabolism-related proteins among the different experimental models.
Highlights
Induction of xenobiotic metabolism in mammalian liver is regulated by a set of nuclear receptors among which the aryl hydrocarbon receptor (AHR), the constitutive androstane receptor (CAR) and the pregnane-X-receptor (PXR) are the most prominent ones, as for example reviewed by Honkakoski and Negishi (2000), Kobayashi et al (2015), and Kohle and Bock (2007)
This study was aimed at comparatively analyzing the hepatic levels of a selection of cytochrome P450 (CYP) enzymes and transporters relevant for drug and xenobiotic metabolism between different species, as well as between the in vitro and in vivo situation
The following experimental models were chosen, partially using archived tissue samples from previously published animal studies (Heise et al 2015; Marx-Stoelting et al 2017; Rieke et al 2017; Schmidt et al 2016): (1) male Wistar rats, (2) male C57/Bl6 wild-type mice, (3) transgenic male CAR/PXR-humanized mice in C57/Bl6 background, (4) transgenic FRG-KO mice with livers repopulated by human hepatocytes, (5) cryopreserved human primary hepatocytes, and (6) differentiated human HepaRG hepatocarcinoma cells
Summary
Induction of xenobiotic metabolism in mammalian liver is regulated by a set of nuclear receptors among which the aryl hydrocarbon receptor (AHR), the constitutive androstane receptor (CAR) and the pregnane-X-receptor (PXR) are the most prominent ones, as for example reviewed by Honkakoski and Negishi (2000), Kobayashi et al (2015), and Kohle and Bock (2007). While many CYPs are part of the biosynthesis and metabolism of endogenous substances such as hormones, bile acids and vitamins, the CYP family 1, 2 and 3 members constitute major players in the oxidative metabolism of xenobiotics (Martignoni et al 2006; Williams et al 2000). The CYP2A subfamily includes three human, three rattine and four murine isoforms. Even though CYPs are classified across species, minor differences in the amino acid sequence of the protein may lead to drastic changes in substrate specificity and catalytic activity. As for CYP2A, the substrate specificities differ greatly between human and rodent CYP2C isoforms. The subfamily CYP3A recognizes a very broad range of substrates and is, very important in drug and xenobiotic metabolism. It was estimated that together, CYPs are involved in the metabolism of 70–80% of all clinically used drugs (Sutton et al 2010)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
