Abstract

CYP2E1-inducing capacity of xenobiotics was determined in cultured hepatocytes on the basis of enzyme activities (chlorzoxazone 6-hydroxylation and 7-ethoxycoumarin O-dealkylation) and protein levels. Hepatocytes in culture showed rapid loss of CYP2E1 enzyme during 72 h. CYP2E1 inducers (ethanol, dimethyl sulfoxide, acetone, isopropanol, pyrazole, and imidazole) were able to prevent the fast decrease of the activities and protein levels of CYP2E1 enzyme. Imidazole was found to be the most effective inducer in rat hepatocytes, and it was selected as a reference in subsequent experiments. The effect of GYKI-47261 [6-(4-aminophenyl)-8-chloro-2-methyl-11H-imidazo[1,2c] [2,3]benzodiazepine], a new AMPA [2-amino-3-(3-hydroxymethylisoxazole-4-yl)propionic acid] antagonist drug-candidate, was also tested in the in vitro system. On the basis of enzyme activities and CYP2E1 protein content of rat hepatocytes, GYKI-47261 was considered as a potent CYP2E1 inducer. Furthermore, it was more effective than imidazole, since 10 μM GYKI-47261 produced the maximal induction, whereas 500 μM imidazole brought about the maximal response. Human hepatocytes were more sensitive to GYKI-47261 than were rat cells. In rat hepatocytes, 10 μM caused maximal increase, whereas 0.01 μM produced the highest induction in human cells. Elevation of CYP2E1 gene transcription as the mechanism of induction caused by GYKI-47261 can be excluded. It seems to act mainly on stabilization of CYP2E1 enzyme protein, whereas the role of stabilization of CYP2E1 mRNA can be considered negligible. Although the imidazole part of GYKI-47261 can explain its CYP2E1-inducing capacity, the other part of the molecule must contribute to the final inducing potency.