Abstract
Addition of [3H]-benzo(a)pyrene to the perfusion medium of isolated rat livers results in irreversible binding of radioactivity to DNA, RNA and protein. Binding to DNA accounted for about 0.1% of the total radioactivity which was bound in livers from animals treated with oil or saline and was increased by a factor of 3–5 after pretreatment of the animals with β-naphthoflavone or with phenobarbital. When the inhibitiors of monooygenase activity, α-naphthoflavone or metyrapone, were present in the perfusion medium, irreversible binding was reduced in livers from both β-naphthoflavone- and phenobarbital-pretreated animals, irrespective of the inhibitor used.
In livers from animals treated with oil or saline protein and a RNA fraction containing tightly associated protein were able to bind [3H]-benzo(a)pyrene metabolites to about the same extent but after induction by pretreatment with β-naphthoflavone binding to the RNA fraction was enhanced to a much higher extent than binding to the protein fraction. Pretreatment with phenobarbital did not result in an increased irreversible binding to RNA and protein.
A considerable amount of 15–25% of the total radioactivity added to the perfusion medium was excreted into the bile after treatment of the animals with the tested inducers of monooxygenase activity compared to an excretion of 3% in animals treated with oil or saline.
The results indicate that nucleic acid and protein adduct formation in the liver is controlled by the action of the cytochrome P-450-dependent monooxygenases.
Zusammenfassung
Nach Zugabe von [3H]-Benzo(a)pyren zum Perfusionsmedium der isolierten Rattenleber wird eine irreversible Bindung von Radioaktivität an DNA, RNA und Protein beobachtet. Die Bindung an DNA betrug in Lebern von öl- bzw. kochsalzbehandelten Tieren etwa 0,1% der gesamten gebundenen Radioaktivität
Nach Vorbehandlung der Tiere mit β-Naphthoflavon oder Phenobarbital stieg die Bindung an DNA um den Faktor 3–5 an. In Gegenwart von α-Naphthoflavon oder Metyrapon als Inhibitoren der Monooxygenase wurde die irreversible Bindung sowohl nach β-Naphthoflavon als auch nach Phenobarbitalvorbehandlung geringer.
In Lebern von öl- bzw. kochsalzbehandelten Tieren wurde etwa gleich viel [3H]-Benzpyren pro mg an Protein und an die RNA-Fraktion, die noch fest assoziiertes Protein enthielt, gebunden. Nach Vorbehandlung mit dem Induktor β-Naphthoflavon wurde die Bindung an die RNA-Fraktion in erheblich größerem Ausmaß gesteigert als diejenige an die Proteinfraktion, während nach Vorbehandlung mit Phenobarbital die Bindung an RNA und Protein nicht anstieg.
Gegenüber einer Ausscheidung in die Galle von 3% der gesamten ins Perfusionsmedium eingesetzten Radioaktivität bei Lebern von öl- bzw. kochsalzbehandelten Tieren stieg die biliäre Elimination nach Vorbehandlung mit den untersuchten Induktoren der Monooxygenase auf 15–25% der eingesetzten Benzpyrenmenge an.
Die Ergebnisse sprechen dafür, daß die Bildung von Nucleinsäure- und Proteinaddukten in der Leber durch die Aktivität der Cytochrom P-450-abhängigen Monooxygenasen kontrolliert wird.
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In part subject of the doctoral thesis of Erik Klaus, Fachbereich Biologie, University of Mainz
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Kahl, G.F., Klaus, E., Jonen, H.G. et al. Enzymic control of irreversible binding of metabolically activated benzo(a)pyrene in perfused rat liver by monooxygenase activity. Arch. Toxicol. 39, 149–158 (1977). https://doi.org/10.1007/BF00343282
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DOI: https://doi.org/10.1007/BF00343282