Ultrastructural and biochemical alterations induced by tryptophan pyrolysis products on rat hepatocytes in primary culture. I. Action on the transcriptional process.
Adult rat hepatocytes in primary culture were used to study the effect of tryptophan pyrolysis products on the transcriptional process. Hepatocytes were treated with 1, 5 and 10 micrograms/ml of 3-amino-1,4-dimethyl-5H-pyrido-[4,3-b]-indole (Trp-P-1) or 3-amino-1-methyl-5H-pyrido-[4,3-b]-indole (Trp-P-2) for 2 and 4 h. The ultrastructural study revealed the appearance of nucleolar microsegregation accompanied by a reduction in peri- and interchromatin fibrils and granules in hepatocytes exposed to 10 micrograms/ml of each pyrolysate for 1 or 2 h. Biochemical investigation showed that the incorporation of [3H]uridine into nuclear RNA of treated hepatocytes was strongly decreased. Time- and concentration-related inhibition have been established; however, the inhibitory effect of Trp-P-1 was always superior to that of Trp-P-2. The determination of Mg2+-dependent RNA polymerase activity in an in vitro system functioning with isolated rat liver nuclei incubated in the presence of Trp-P-1 or Trp-P-2 showed a 40% inhibition of this activity. After a 1-h exposure of hepatocytes to 5 and 10 micrograms/ml of Trp-P-1, the recovery of RNA synthesis capacity was complete by 2 h and that of normal ultrastructural aspect was achieved within 4 h. All these results indicated that Trp-P-1 and Try-P-2 acted at the nucleolar level by a blockade of pre-rRNA synthesis and at the extranucleolar by decreasing the ultrastructural RNP responsible for hnRNA synthesis.
D000818:Animals; D002243:Carbolines / Q000494:pharmacology*; D002273:Carcinogens / Q000494:pharmacology*; D002478:Cells, Cultured; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D007211:Indoles / Q000494:pharmacology*; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008854:Microscopy, Electron; D051381:Rats; D011919:Rats, Inbred Strains; D014158:Transcription, Genetic / Q000187:drug effects*
D002243:Carbolines; D002273:Carcinogens; D007211:Indoles; C019133:3-amino-1-methyl-5H-pyrido(4,3-b)indole; D012321:DNA-Directed RNA Polymerases; C019132:3-amino-1,4-dimethyl-5H-pyrido(4,3-b)indole