title: Pharmacokinetics explain in vivo/in vitro discrepancies of carcinogen-induced gene expression alterations in rat liver and cultivated hepatocytes.
abstract: Cultivated hepatocytes represent a well-established in vitro system. However, the applicability of hepatocytes in toxicogenomics is still controversially discussed. Recently, an in vivo/in vitro discrepancy has been described, whereby the non-genotoxic rat liver carcinogen methapyrilene alters the expression of the metabolizing genes SULT1A1 and ABAT, as well as the DNA damage response gene GADD34 in vitro, but not in vivo. If the collagen sandwich cultures of hepatocytes really produce false-positive data, this would compromise its application in toxicogenomics. To revisit the putative in vivo/in vitro discrepancy, we first analyzed and modeled methapyrilene concentrations in the portal vein of rats. The relatively short half-life of 2.8 h implies a rapid decrease in orally administered methapyrilene in vivo below concentrations that can cause gene expression alterations. This corresponded to the time-dependent alteration levels of GADD34, ABAT and SULT1A1 RNA in the liver: RNA levels are altered 1, 6 and 12 h after methapyrilene administration, but return to control levels after 24 and 72 h. In contrast, methapyrilene concentrations in the culture medium supernatant of primary rat hepatocyte cultures decreased slowly. This explains why GADD34, ABAT and SULT1A1 were still deregulated after 24 h exposure in vitro, but not in vivo. It should also be considered that the earliest analyzed time point in the previous in vivo studies was 24 h after methapyrilene administration. In conclusion, previously observed in vitro/in vivo discrepancy can be explained by different pharmacokinetics present in vitro and in vivo. When the in vivo half-life is short, levels of some initially altered genes may have returned to control levels already 24 h after administration.
authors.affiliation: Leibniz Research Centre for Working Environment and Human Factors at Dortmund TU, Dortmund, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Schug
authors.forename: Regina
authors.initials: R
authors.lastname: Stöber
authors.forename: Tanja
authors.initials: T
authors.lastname: Heise
authors.forename: Hans
authors.initials: H
authors.lastname: Mielke
authors.forename: Ursula
authors.initials: U
authors.lastname: Gundert-Remy
authors.forename: Patricio
authors.initials: P
authors.lastname: Godoy
authors.forename: Raymond
authors.initials: R
authors.lastname: Reif
authors.forename: Meinolf
authors.initials: M
authors.lastname: Blaszkewicz
authors.forename: Heidrun
authors.initials: H
authors.lastname: Ellinger-Ziegelbauer
authors.forename: Hans-Jürgen
authors.initials: HJ
authors.lastname: Ahr
authors.forename: Silvia
authors.initials: S
authors.lastname: Selinski
authors.forename: Georgia
authors.initials: G
authors.lastname: Günther
authors.forename: Rosemarie
authors.initials: R
authors.lastname: Marchan
authors.forename: Meinolf
authors.initials: M
authors.lastname: Blaszkewicz
authors.forename: Agapios
authors.initials: A
authors.lastname: Sachinidis
authors.forename: Andreas
authors.initials: A
authors.lastname: Nüssler
authors.forename: Axel
authors.initials: A
authors.lastname: Oberemm
authors.forename: Jan G
authors.initials: JG
authors.lastname: Hengstler
mesh_terms: D000612:4-Aminobutyrate Transaminase / Q000235:genetics; D000818:Animals; D000943:Antigens, Differentiation / Q000235:genetics; D015239:Arylsulfotransferase / Q000235:genetics; D002273:Carcinogens / Q000493:pharmacokinetics* / Q000633:toxicity; D002478:Cells, Cultured; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006207:Half-Life; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D008701:Methapyrilene / Q000493:pharmacokinetics* / Q000633:toxicity; D011518:Proto-Oncogene Proteins / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
chemical_list: D000943:Antigens, Differentiation; D002273:Carcinogens; C489287:Ppp1r15a protein, rat; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D008701:Methapyrilene; D000612:4-Aminobutyrate Transaminase; D015239:Arylsulfotransferase; C573795:Sult1a1 protein, rat